How much black tar heroin do you put in the spoon to shoot it up?

It depends on your tolerance. Remember that injecting heroin is a more effective method of getting high than smoking or snorting, so you will use less when injecting than you would in the other methods. Also, since it's a street drug you can never be certain about the strength and purity... at one point I was buying from the same source every single day for over a year, and there were subtle differences in every batch. That sh*t happens, it doesn't mean that it's a bad source... it's obviously not made in a factory that can test for quality control so variation in purity is to be expected.

To be safe, start off with a little piece about half the size of a match head. Yeah, I know it's small but if it's your first time you don't know how you are going to react to the amount yet so it's better to be safe than sorry. You can always take more but you can never take back what you did.

I'd recommend that every time you buy more, whether it's from the same source or not, start off with less than you'd normally do so you can test the batch and be confident that you aren't going to OD. Nothing ruins a high faster than waking up in the ER puking your guts out from some Narcan. ;)

I personally wish you wouldn't start injecting in the first place... it's a long downhill journey once you start. But I'm not going to lecture you on it, because I'm a dope addict myself. I'm facing the consequences right now though, I'm 18 and looking at 3-5 years in prison. Part of me wishes I never picked up the needle, and another part wishes I never got caught so I wouldn't ever have to put it down. I wish you the best, and be safe!