Multiple passwords, usernames, wp accounts?

After a wp hiatus of several years I’m back. Yay. my newest wp site is accessible for edits, etc. with username and password. I’m confused by the other wp.com and wp.org accounts, each of which has its own username and passwords.

Now I’d like to load images from my cellphone phone to my wp site and can’t seem to access the site with my current usernames and passwords. How do I link my cellphone to one of my existing wp.org or wp.com accounts directly? I am using an Android LG