Getting my bearings

This is the first time using a website like this for me and im trying to figure everything out so i have a few questions

1. What type stuff do you put in a blog?

Ive read a few of them to figure out what all type stuff to put and it seems fairly general but im also trying to figure out what all you shouldnt put

2. Is it worth it to try to figure out how to code with http coding if im not trying to publish layouts or other things?

I know generally it wouldnt be bad but ive found recently ive developed a lot of other time consuming things and im not sure if this would be something worth being one of them.

3. Why cant i add a pfp?

I tried adding a perfectly square one and it just didnt add right, it was a png so it should have worked but for some reason it isnt, what should i do?

4. Finally, is there any etiquette that isnt expressly stated that i should follow?

I mean i get "be nice, be respectful" but i mean stuff like words i ought to censor, topics that might offend people, that type thing. Most of my life i havent had to worry about that type stuff because i never used these blog type websites but i figure i ought to figure that out before it bites me.

Thank you for reading, your advice is very much welcome and appreciated!