Welcome!
Just write what you know or do what you like. I'm new like 10 days or so into posting and it takes consistency and luck. One of the things I have enjoyed doing is going to things like #beersaturday, #colorchallenge and #fff or #foodfightfriday. These can be good places to get your feet wet so to speak. Pretty easy stuff, just use the appropriate hashtags and write an appropriate post with pics.......beer, food, colors.
Also might be worth searching for contests in the search bar. There are some pretty regular ones hosted by people like @vdux whose current contest is Haikus. Here!
If you don't want to post just comment on other posts, meaningful though....add something...not just "nice pic" although that may sometimes suffice...
Well, good luck!