What am I allowed to include in my blog?

[해나~]

Hey everyone! I recently started my own blog, but I'm wondering what I am allowed to post and what I am not. I've recently read an article about someone who got sued for uploading a picture that was apparently copyrighted. I know that it's dangerous for bloggers to upload pictures from google because of unspecified copyrights. In that case, how would I know if I could use that picture or not? Where could I find pictures that I could upload onto my blog?

ALSO
Is it okay to mention brand name stores like Forever 21, H&M, and Hot Topic? Is it okay to upload pictures of items that they carry in their stores?
What am I allowed to say about their items? (What are my restrictions?)

If there's any other information I should be aware of to avoid lawsuits, please let me know!!

Thank you very much in advance.