Hey there Melissa! Not to fear, tea can become unscary quite rapidly.
To answer your question about quantity, generally 1 tsp of tea leaves per 1 cup of water (8-12 fl oz) is the way to go. I have heard of using only 1/2 tsp for some teas, but I don't think that will apply to any of the teas you have. Secondly, are you keeping an eye on how long your tea steeps? For black teas, the rule of thumb is to steep in boiling water for 5 minutes. I have found, however, that adagio's flavored black teas require only 4 minutes. For your green teas, 3 minutes at 180 degrees (not that I really follow the temperature rule, but it's good to know) is the recommended time and temperature. Oversteeping is the reason teas get bitter. If your tea is still too bitter for your taste after only 5 minutes (or 3 for the green), you can experiment with using less tea or steeping less time (that's how I found out that adagio's flavors are best at 4 minutes).
Once your tea is brewed, any type of sweetener or such is cool. It depends on your taste. I'd recommend tasting it first without anything in it, just so you know the original flavor of the tea. Sugar sweetens well without adding its own flavor, but honey goes really well in green tea. Especially when your throat hurts. Personally I don't usually use milk/cream in my tea, but when I do, it's only black tea. Don't know if anybody's put milk in green tea, but it seems like that would be nasty. It does help, though, if you've oversteeped your tea by accident. The milk counteracts the bitterness because it binds with the tannins in the tea and neutralizes them (that's what makes tea bitter... I think... could be remembering that wrong, as it is late and I am sleepy).
I hope you will end up enjoying your teas. Yeah, preparation's a little overwhelming at first, but by following a few general guidelines and experimenting a bit, you can bring it down to whelming. Then you can let yourself be overwhelmed by the glorious taste and fabulously relaxing or invigorating experience of your tea. Wow I sound like a bad brochure writer. But I hope this has helped