a) Central filter installed,
b) In-line filters
You will have the one line "sliced" into two connections - one high frequency ADSL line and the other standard phone line.
You need to have in-line filters installed on each device that is on the same line, because of interfererence.
These can be installed by you, so it's only $37 or so bucks.
If you don't want the ugly filters installed on each device (cordless phone, fax, etc)
then you can get a Central filter installed which you cant do yourself. You will need an electrician or telecommunications person to come out and install that at the front of your house where your box is, or underground (Im not too sure on this).
But if you want the cheaper option, you will need a central splitter to divide the line (share it) - then you need to have filters installed on each device that shares the same line, if you have one phone and one adsl modem, then it's just the one filter.
I could be wrong about all of this, as I dont know many people who have the main central filter installed, as most opt for the in-line filter (those you can see within the home, plugs from the outlet, through the filter, to your device/phone or fax).
Visit tandy or DSE like Winston has said, and get yourself a line splitter and filter (make sure your exchange is enabled for ADSL, your line has been provisioned, and you are ready to receive ADSL before you purchase your ADSL modem or buy any splitters or filters because you might not be able to receive ADSL).