Cream can be whipped with a fork but it's more tedious and takes longer to whip the cream using a fork instead of a whisk or whip utensil.
I once used a fork to whip cream before and it was harder and my hand and wrist hurt more and it took longer to actually get the cream whipped with the fork.
So I bought a set of whipping and whisking utensils to make whipping and whisking cream and other foods easier than using a fork.
I would recommend buying at least a whisk or whip utensil which you can get pretty cheap but if you need to whip cream right now and don't have the utensils to do it properly then you can whip the cream with a fork but just note that it will take a bit longer to whip the cream properly with a fork.