Honestly, you get to know what you like/dislike through experience. I just stumbled across a semi-local dungeon which is big into teaching so it is pretty easy and fun to experience things like wax, fire, bondage/suspension and violet wand play. However, if you have neither partner, friend, nor local community, do research and find things that you can do to yourself. There is a book out there about bondage or BDSM on a budget and takes ordinary things around your house to use in kinky situations. I'm sure you can find it with only a minimal amount of research.
As to safety...Jas Wiseman preached in his 3 day workshop over the weeknd, NO SELF-IMMOBILIZING BONDAGE BY YOURSELF. 95% of all BDSM related fatalaties involved complete immobilization and no one else...this includes things like knocking over candles while flopping to tie yourself down and not being able to get yourself untied while the room around catches fire...
Protocols...each situation and group is different. Some like hard boundaries between Doms and subs, while others are more lax. This site pretty much has people from both persuations, but no one will put you down or judge you based upon a posting or otherwise not invited. If you start playing with someone, just be honest and let them know what you have researched and ask what they prefer for you to do/not to do.
And how to get to know people...read, post, and maybe check out the chat space.
There is my advice :-)