Welcome to steemit!

Here is some information every newbie should know, taken from my website, SteemEHQ - https://steemehq.club/:

The value of an upvote is related to how much Steem Power the upvoter holds, as well as the current market price for the STEEM cryptocurrency coin.
Upvotes are not infinite, but they recharge. The more upvotes a person uses, the less it will be worth next time. On average, each person can give 10 full upvotes per day, because it's also how much upvotes recharge daily. People have to pick between many posts to decide what they're going to upvote, often choosing something they like but also taking profits into consideration. If someone doesn't upvote you, they could be waiting for their voting to recharge.
Your free account started with a borrowed 15 Steem Power. As you earn from your posts and comments, that will be taken away until you're standing on your own feet in the platform.
Remember to both give and take. If people only want to take away from the platform, the STEEM coin will eventually be worth nothing, because then everyone wants to sell while noone would be willing to buy.
If you run into posting limitations, that means you need more Steem Power. It's like a "bandwidth". The more you hold, the more you can do. It recharges, but slowly if you don't have much SP.
Steem Power can be bought, but it can also be delegated (borrowed/lent) using a steemit command. It can be undone by using a similar command too, so the delegator is in complete control.
You can check those bandwidth and voting metrics on the steemnow website.

I have attached a picture from the steemnow website below so you can see what it's all about. Note: I don't own the website.