Hello and Welcome sinacengiz. A few comments to try and help.
How it works: People post stories, information and other topics, other users read those post and vote on the ones we like the most. In some cases, these votes can lead to posts earning Steem.
I am not a Reddit User so I can not answer that.
You can post on any topic that interests you.

Make friends by commenting on other people's posts and also Steemit Chat is a good place to make friends.
Steem Chat
https://steemit.chat/channel/general

Good Luck on your SteemIt Journey!