To EQ all audio sources you'll need to have a receiver/amp with either a tape monitor loop or a pre amp-in/main-out loop. Look for a button on the front labelled 'Tape Mon' or ins and outs on the back labelled pre amp-out/main-in. If you have these you can connect the outs from the amp to the ins on your EQ and then EQ outs go back into the amps ins. If you have a tape deck as well, the EQ's 'tape mon' jacks replace the ones it takes up on the amp, so just plug your tape deck in here.

Just remember that whether you have a tape deck or not, if you hang an EQ off the 'tape mon' loop you'll have to engage the 'tape mon' button/switch for playback with EQ.

If your amp doesn't have these loops you can still use EQ but you may be restriced to one audio component source. So say you wanted to EQ the playback from your CD player, you'd just connect the CD players output into the EQs input, then connect the EQ's output into the amplifiers input (for CD player). Then everything you play through the CD player will be EQ'd.