In twitter, how can you send direct messages to whoever you're following?

[ALESANA]

but they're not following you?

also, how do you retweet?

[Landyhnn]

go to your direct message tap on the side.
then at the top it will say SEND then a drop down list a direct message.

[BrokenAngel]

On the right side on their page, under Actions it says message and block.

Put your mouse over the message you want to reply to and a left-pointing arrow will appear on the right hand side of the message. Click on it and @ plus their name will appear in the entry box and just type your reply.