Hi Kirsty, what Lynda said is spot-on of course. I just recently added my DNA tests to WikiTree so I thought I'd say hi.
At Ancestry you should have a DNA test kit number. Record this somewhere.
On WikiTree, use the drop-down lists located top-right of the screen; under "add" the first selection will be "DNA Test Information". Just follow the cues from there to enter the kit number.
After a day, it shows up on the profiles of your ancestors. If you find an ancestor with other kit numbers on it you can compare them through Ancestry (if they did their test there too) or through GEDmatch (which everyone should do).
I'm sure you will be pleased with the results. I've discovered new cousins and learned a lot.
Cheers from Vermont!