Sepia toning serves two purposes. Firstly, it is an archival process, sepia toning your black and white prints will make them last a lot longer. Secondly, it gives your print an attractive brown finish, that makes them look like a Victorian Christmas card.
Sepia toning is a two-stage process, and will work on almost any black and white print (the exception is prints which are made on colour paper, as many machine prints typically are). The first stage requires the print to be bleached, drop it into the bleach solution and watch until it has almost completely faded (depending on the bleach used this may take up to 5 minutes). Next, wash it for 2 minutes (resin coated paper) or 5 minutes (fibre based paper). Finally, drop it into the sepia solution until the image has returned as a sepia image, then wash thoroughly again.
This technique does not require a darkroom or any specialist equipment apart from two print trays. Toning kits are very cheap and can be used on any traditional black and white print (no matter how old it is).