I have a 1994 Silverado with a 350 TBI and has just over 232K miles. Would using seafoam benefit to clean and how would I put it in? Feedback is much appreciated. 
Why do you think you need to add something. If it still doing fine at this mileage why mess with it.
You could go to the seafoam web site.
Edit: OK, I just looked at your history and see that this is possibly a vehicle being provided to a 15 year old. You asked about dropping gears and other things. I suggest you run all these ideas by your parents and do not abuse this vehicle.
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The instructions are on the can and probably the web site, like @VOLVO_V70 said. And I’m also wondering why do you want to use it?
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It couldn’t hurt, unless you manage to hydrolock the engine. Dosage is on the bottle. For what it’s worth, I’ve had decent success with seaform. I used it on my old Bronco around the 150k mile mark, and it idled noticeably smoother afterwards. I also used it on my old Mustang around the 120k mile mark, and it didn’t make quite as big a difference, but again, it ran a little smoother. For the Bronco, I dumped some in the engine oil, dumped some in the fuel tank, and sucked up a 2nd can into the intake manifold via the power brake vacuum line. For the Mustang I just sucked up a can with random vacuum line. You have to be careful when doing that as it’s entirely possible to suck up too much at a given time and hydrolock the engine.
I’ve never felt the need to try it, but I have read where you had better plan on changing your oil within 100 miles or so of adding it (to the crankcase), because it can loosen up quite a bit of gunk.
I am in the frame of mind that at 232K, if it’s running fine, I’m not sure that I would try it, but that’s just one mans opinion.
What you’re already doing is obviously working. Why mess with success?
Unless, of course, you’re having some problem that you didn’t mention… ?
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To the good advice and many questions already posted, I want to add an additional point:
Depending on the mystery problem that this vehicle might have, Seafoam can be added to the fuel supply or to the oil in the crankcase. The approach that one uses is determined by the nature of the problem that you are trying to resolve.
What–specifically–is the problem that the OP is experiencing with this truck?
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Others may disagree, but common sense would tell me that using Seafoam would in fact do long term damage to your CATs by clogging them up. This depends upon how much carbon deposits you already have built up in your engine at this time. At 232K miles, I would guess a lot.
They may advertise that it’s safe, but where do those carbon deposits actually go? Does you engine pass 100% of it through the CATs or do they in fact tend to tend to clog them over time with re-use?
Personally, I wouldn’t use it UNLESS I had the CATs off at the time I used it. But hey, that’s just my two cents.
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It idles rough. Which I guess it has always done. And shifts somewhat hard from 1-2. And I feel lack of power that it should have.
Whens the last time you replaced plugs? Spark plug wires? My '95 Suburban had a bad set of wires, caused rough running and acceleration.
What’s been checked/done so far?
Have the ignition components been changed?
Has the compression been tested?
Has it been checked for a vacuum leak?
Has the throttle body been cleaned?
Are there or have there been fault codes?
Has any maintenance been done on it?
It’s getting long in the tooth, and it may be simply variations in cylinder compression, but it’s also possible that you have a carboned up throttle bod, a carboned up EGR valve, a weak ignition component, or even a vacuum leak. And if you’ve had a check engine light it may point toward a mass airflow sensor, an oxygen sensor, or who knows what else. Eliminating these possibilities is a better approach IMHO than trying seafoam.
The OP has claimed to 15 years old. Shouldn’t the OP be in school instead of on the internet?
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He might be typing from his desk…
Besides, he’s probably learning more here. 
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I’ve used it on two cars and it never did any damage to the cats. You use it two ways, in the gas and through a vacuum hose to go directly to the throttle body. It does a nice job of cleaning out the throttle body but smokes like hilly heck until it burns off so make sure your neighbors don’t call the fire department.
Seafoam might just help a rough idle if it is added to the fuel supply.
As to those hard shifts, I strongly recommend that you NOT add Seafoam to your transmission fluid.
Instead, you should consider taking the vehicle to an independent trans shop for a trans fluid and filter change.
[quote=“devallision2, post:9, topic:100523”]
shifts somewhat hard from 1-2. [/quote]
Try AutoRX with a transmission fluid change to help clean any shift solenoids that may be sticking, driving 1000 miles and then draining and refilling the transmission with all synthetic fluid if it doesn’t have it already.
NOTE: The synthetic change out is optional since you’d have to either change out the fluid in the pan enough times to dilute it to less than 5% non-synthetic or find a way to flush it completely for (I’m guessing) 10-15 quarts in the transmission, which isn’t cheap @ $10/qt.
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I am not sure, awhile ago for sure. It is getting them done this summer
Does it work well with the TBI being cleaned?
Won’t learn anything about cars in English 
It needs a lot of care for my dad left it sitting for 3-4 years after he got his new Truck. He doesn’t want me putting any money into it for it being that old but, that’s the only way it’ll get back to running like the beast she was when it was our daily. It is soon to be my daily here in may and I think with the right care she will run great. I’m thinking seafoam through brake vaccum line and TBI as mentioned and new spark plugs as well as an oil change after the seafoam.