All I can think of is to say something threatening to someone. I wouldn't recommend it
yes
The more companies you follow on Twitter, the more companies Twitter will recommend to you.
In New Twitter, the "Messages" tab located at the top of the page along from the search bar is where your Direct Messages are located.
onyour wall
Nope
It stands for Check Your Direct Messages.
she has to follow you
You may send a tweet (or @reply) to anyone on Twitter; you certainly don't have to be following them! Following a Twitter user just means that all their tweets appear in the "timeline" on the home page of Twitter when you log in. (Along with your tweets and the tweets of anyone else you may be following.) To follow someone, go to their Twitter page and click the "follow" button. Anyway, to send a tweet to any Twitter user, just include an @ sign followed by the username of the user you want to send the tweet to. For example, if you want to send a tweet to the user with the username JohnSmith, include @JohnSmith in you tweet.
Twitter is a micro-blogging site, it allows 140 character messages while e-mail allow long messages and file attachments.
Find their Twitter username and begin your tweet with it.
You need unlimited data for Twitter to be free.
Assuming you are using the new version of Twitter, go to the top bar where it says "Messages". Once there, on the side it will show your message. Click it, and it opens up the conversation on the right side. If you are using the old Twitter, then go to the tab on the right side of your home page that says "Direct Messages" and it will display your messages down the page.