Hi there! I'm super excited that we managed to intrigue you! I haven't had a lot of tumblr rp experience myself but I can try my best to differentiate the two.
Outside of where things are hosted (tumblr vs a forum) at their core they are very much the same. You still write a post and then your writing partner(s) will reply. I'd say the biggest difference is timing. Tumblr RP is very much instantaneous while Forum rp is a bit more gracious with response time. You don't have to reply right away and sometimes it can take people a week or more to give a response and that is okay! Granted, Forum RP does have a rapidfire option where people just focus on instantly replying back and forth but that typically isn't the norm.
I think maybe posts are a bit longer on forums as well? I've seen people write anywhere from 100 words to somewhere up in the thousands as far as word count goes. On Oleander specifically, we don't require a word count. So you can write as much or as little as you like.
Oh boy this is getting Long....I’ll stick the rest under a Read More tag so please continue there.
As far as the application process goes, that will vary from site to site. But for Oleander, we have a two part process. The first is filling out a profile with information such as a Character's name, where they live, and what their occupation is. There's also a section there where you'll do an overview of their personality and family history. It doesn't have to be anything long just enough that someone reading it will have a good sense of your character.
The second part of the process is filling out a Shipper, sometimes called a Plotter. That's where you can go a bit more in-depth. You'll give a break down of what your character looks for in Friends/how they are as Friend, what sort of people or things would make someone their Enemy, and then what they look for in a Romantic partner. It basically gives people a run down of how your character acts to let them try to figure out how well their own characters would mesh with yours.
After those two parts are done, Staff looks over your application and then will sort you into the correct member group ~~ We have a registration guide that can walk you through it if you get lost or a Staff member is always happy to help! (I was full of questions when I first joined a form RP myself. I know that there is a lot to take in sometimes so we do our best to try and make it not so overwhelming....)
Now for Canons ~ Outside of what little descriptions we've given (and the Guilds for the Guild Masters as we had to build them) everything is entirely up to you! You can choose your face claim, species, age, family, history, personality, etc. If you pick up a canon, you'll help us shape them - Just as every member will help us shape the world we're all creating together.