I'll try to help you with this answer, so just tell me if you need further help.

Upvoting something does help you to earn currency, but it is not yours until they pay you in your wallet.

So you are asking about 2 separate things. Upvoting is just one way to earn money as a "curator", the other way to earn money is being an "author" of both posts and comments.

So I'm going to upvote you right now to make this explanation real to you. I just voted you $0.01. Now what that means is that steemit will pay out a total of $0.01 in 7 days. You as the author will get at least 75% of that and I as the curator can get as much at 25% of that vote. In 7 days, they will pay that out and it will be paid 1/2 in SBD (or 0.005 total SBD between the two of us) and the other half in US$ equivalent of STEEM... You will know what happens as you start getting these payments and they are automatic after 7 days.

Now you wallet is simply where they store up... They are an accumulation of all the things you have earned so far (but remember it takes 7 days for anything to show up). What you are seeing with the .001 STEEM is what they gave you when you opened the account.

Finally SP is it, its the one to own ultimately (remember though it will change in price a lot)... Its what you want to have because its what give you earnings from just your votes. Right now you don't get much for your votes, but as you get bigger your votes get bigger an therefore your earnings get better. I am working on putting together what you can do with your SBD, but I am either using @bumper or converting it into more SP (depending on the conversion price being favorable to me or not).

I think you can never overthink anything ;).. It takes some brain cells to wrap your mind around this. I would say that you shouldn't get frustrated, because while it is simple once you understand it, it is very hard to grasp in the beginning. So giving it some thinking is a good thing.

Just ask me questions you have at any time, but if you want to learn it, I promise you that I can teach it to you. :)