What kind of pc do you have? If you have anything less than a gtx980ti, 1070 or better ( rx470 480 570 580 amd equivalent) I don't believe its very profitable.
The easiest way to get started is to choose a mine-able coin and go to the website of a pool mining that coin. There will be instruction on how to get started in the help section.
An example to get you started would be siacoin, it is gpu mine-able for at least the next year and although the profits wont be high it's a good way to get started.
Hope this helped
i have a macbook air
You can't mine profitably on a macbook air, additionally you might damage it if you do so i wouldn't recommend it.
yeah, you're going to have to find a coin with a lot of low hanging fruit for that... Most people buy seperate computers / cards to mine specifically