Nia, I don't have firsthand experience with this, but from what I've heard it's important to wrap the cake tightly in plastic wrap (no air!). Most recommend wrapping it twice with plastic wrap and then placing it in a Ziploc freezer bag and/or wrapping it in aluminum foil. I bet Skwigg will have good advice as she freezes a lot of desserts. :)
Nia, slice it and then if it has frosting, get the slices cold in the refrigerator or freezer. You can put them on a cookie sheet or whatever works. Firm, cold frosting keeps the plastic wrap from sticking. Wrap the individual slices in plastic wrap and then put them in a bigger Ziploc freezer bag. They'll be fine for a few months. When you want one, just set it out on a plate for 30 minutes of so to let it come back to room temp.
Anything with fat in it freezes really well - cookies, cake, pie. I do cake slices and moist or frosted brownies with the plastic wrap and then plastic bag. It keeps them from freezing together. Cookies you can just put in a freezer bag. They don't tend to stick. Messy, fruit pie kind of desserts that aren't going to stay together I put in small disposable tupperware containers and stack them in the freezer.
It just occured to me that biscuit is something completely different in US. I guess it would be something like cookie cake? Thanks Skwigg - followed your advise and freezed half of it, cutting individual slices first.