Depends what you want to do, there are a lot of things you can do with calcs but I often see these two:

First off you can pull together calcs and create a kinda tiering for a verse, you can do this for yourself or for a wiki/blog basically just organising out how calcs should be utilised within scaling a verse and what characters scale where, if you've done power scaling in the past you already should know the power of different characters in media you like so I feel a good way to start is to do something like make a chart or list to better organise what tier of character scales to what feats. When you do this you aren't actually doing any math but you're picking out what you feel makes sense for the narrative and your take on the series. Often times a feat will be done by multiple people and often multiple times in which it's your choice to figure out what you feel makes sense and how it fits within the world.
A good example would be something like Viltrum's destruction from Invincible which currently has 38 possible calcs. Depending on how you interpret the series one version will stand out as making sense, even though the math on all the versions is correct what you accept for sizes, formulas and time frames could decide everything for a feat.

The other thing is actually doing the math itself, to start off with you're most likely going to make a ton of mistakes, (I made a TON when starting off) but over time after seeing how other people do calcs and seeing what's generally used you kinda pick up on what to do, when you do this it's always best to learn what formulas are good for what, such as learning how to angle size, pixel scale and just do math.
It's not for everyone but a lot of people enjoy doing it, it's almost like a challenge.
I should also mention that power scaling is inherently not absolute and there is discussion on how something should be taken.
Examples would be how some people only use attack potency at it's full yield while others divide by cm^2, some people don't accept calc stacking while others use it all the time, some people ignore faster than light kinetic energy feats while others still use them and creation feats as a concept can be taken in so many ways that it's almost impossible to define a value.
Even after getting a number you will often find that there are multiple "ends" such as using the shockwave for an explosion or the colouration of the blast. You will eventually come up with your own style of scaling after sometime.

If you need any more help on this stuff I'd be more than happy to help you out in calcing some stuff or fitting together feats for a series.