How to use the proper calculations necessary to use resistance wire in a project ?

I have a few projects in mind that require the use of resistance wire for a heat source . Possibly stranded  and coiled wire . One angle , I know the maximum power and need to know what size of wire could acheive a disired temperature . Then coming in with known element size and figuring out a power source capable of a desired heat range . I have been exposed to ohm's law in a industrial controls class , so I now know enough to be dangerous. Just not sure on how to apply it. Thanks

If you know the power and the voltage available, then, since Power = V^2/R, R=V^2/power.

From tables of the resistance per unit length of your wire - there are oodles of sites out there with such, they will say "such and such wire has a resistance of 0.5 Ohms/metre, calculate what length will satisfy your R requirement by Length = R / resistance per length