I haven't looked up any recent info on this or on possible changes recently, but here is basic info off the top of my head:
It is only okay to do in the senate as the house doesn't have bylaws supporting it. In the senate you can speak as long as you want until you agree to yield the floor. Normally business goes about as usual, but if you want, you can refuse to yield the floor as long as you keep talking. You don't even have to talk about the subject at hand and could literally talk about anything, though most of the time it does go fairly on topic especially with a modern filibuster because they are all aware its on TV and being reviewed in social media.
Filibusters do not achieve a great goal other than drawing attention to themselves, the people involved, and the issues at hand UNLESS there is a lame duck senate close to the end of its term. If, say, there are two days left to the end of a term and a senator wants to prevent the current congress from voting on a particular issue (perhaps because he believes the new senate would vote differently and in his favor), he could filibuster for the entire time period until the new senators were set to be sworn in, thereby preventing a vote from the existing senators and putting the issue into the hands of the new group. This is basically the only strategic move to a filibuster that has a real chance of working.
Again, this info may be a bit dated, and someone else might have better info because I haven't gone over this since grad school.