What are you intending to record with your microphone? Additional audio to the camera sound, as you film? --or are you intending to add narration afterwards in the computer?
If it's the former, then you are going to need an external audio recorder for your microphone to connect into, and it's not going to be easy to find one for less than £20.
Olympus do the cheapest reasonable quality recorders. Try and look for something like the WS100, or WS200S.
Or you might find a secondhand Minidisc recorder at a reasonable price.
You are going to have to syncrhronise the remotely recorded audio with the camera audio somehow in your editing program, but it's not too bad if you follow a few simple rules.
Golden rule is to make an audio marker at the start of your recording --that's what the pros use the 'clapper board' for -then you just line up the recordings with the same starting 'clap'point.
If you are intending to record long sequences in one go -like the wedding videographers do for example - then you may need to match the two recordings. I posted a procedure here:
My Video Problems :: View topic - Synchronise external and camera audio tracks. a couple of years ago. It's not as bad as it first appears, honest!
But as I said at the start, it all depends what you are trying to do?