EDIT: It has been pointed out to me that another good source of documentation is here.
For the most part, the documentation is very good -- but the Discord chatroom is far from "intuitively obvious to the most casual user" and there were a couple other places where I actually had to think. So . . . . here are a few additional hints that would have helped me.
TO REGISTER: You can send either STEEM or SBD to banjo and minnowsupport. If you don't have either yet, post that fact in #general and I'm sure that someone will take care of you.
TO BECOME A MEMBER: When you are unlocking your account on Streemian, use the second method. The first method hasn't worked correctly for a number of people.
In order to direct message (DM) someone (like @aggroed to become a member), you must first be friends with them -- which requires them to accept your invitation. Start by clicking on the people icon in the upper left. Assume that it may take a little while for your invitation to be accepted so you probably want to do this sooner rather than later.
In order to upload a file (like a screenshot), follow the instructions here.
The screenshots required are those of your registration with Streemian and SteemVoter.
YES! You should be concerned when you are asked for your keys; however . . . .
Streemian uses the new delegation method so your key never leaves the browser. This is the correct best practice and hopefully SteemVoter will move to this method in the future.
If you're going to become a member (and you certainly should), you should also apply to be a greeter. This post is my application for greeter . . . . (and I hereby "promise to help users that work with the community").
You definitely should follow (and up-vote) the witnesses, greeters and anyone else you see being particularly helpful as community support should be rewarded to create a virtuous circle.