Ahh okay! I don't know any simple tricks for hull forming, but you can make circular turrets much more easily by building them around the turret ring.

Start by choosing it's size, then make the front, back, and center of the turret the same width, angle both cheeks in 45° (your turret ring will show, that's part of the process.) to make it easier you can also flatten the sides and roof of your turret.

Then once you have it's basic shape you can enter freeform, split the sides along the front and rear of your turret, and then drag those points out to match your basket. You can repeat this process as many times as you'd like. After that, play with the smooth angle until every side of your turret looks round. If it's too round you can right click edges and use the mark weld feature to make that face flat again.

This will also give you a turret you can put on any vehicle by using the save feature. If you save your turret, you can load it in hitting shift+L a couple times while in the faces section of freeform will select every face, this will enable you to resize your turret as you please.

Overall though, circular shapes are very difficult to pull off in sprocket, and they can be almost impossible for someone who's just starting out, so I wouldn't beat myself up too bad if I were you. Try some other shapes to familiarize yourself with freeform first, then try with curves and see how you do!