Easy job - honestly!
Just need patience and a decent drill bit and possibly masking tape (although once done a few times you needn't bother with masking tape.) The drill bit should be a tile cutting drill bit - best ones are at your local tile shop rather than building supplies.
1. Watch for any pipes or wires that are under the WC - usually aren't any but if you're new to this best to be safe. If they are don't drill holes too deep or use too long a screw or bolt.
2. Establish exactly where you want to drill the holes.
3. Remove WC then refit as a dry run. This time fit a couple of pieces of masking tape in rough area of hole. Re-measure (measure twice cut once as the saying goes). Make pencil marks on masking tape.
4. Check and dry run again if necessary. Check also that loo doesn't wobble and if it does, make up where necessary with thin pieces of wood or whatever (best not to use cardboard as this looses rigidity when wet).
5. And check again until you're totally comfortable with fit.
Then the easy part - drilling holes.
Masking tape should have pencil marks on in correct places.
With drill bit in battery drill, press against mark and turn drill very slowly. Keep going, taking your time and press further into hole. It will be tiny to begin with but won't take too long to get larger.
Remove masking tape.
Once hole is 6mm wide then you can change drill bits for the floor below.
If concrete floor make sure hole is deep enough for screw or bolt. If it needs to be wider (e.g. for bolt) then you can use the next size up of masonry bit one millimetre at a time until hole is wide enough.
If wood floor make sure you don't drill through all the wood - best to let a wood screw bite into the floor as it will be a stronger fit.
Finally, don't tighten bolt or screw too tight - until it just grips - or you'll greatly risk cracking the pan (something I learned a few years ago!)
I admit it's petrifying first time, but give yourself time and there's no real difficulty with the right bit.
Good luck.
