Soil and Nutrients

My friend gave me some seeds and black magic potting soil. I was wondering if I should mix the soil with anything else and what nutrients I should buy? I would also like to ask if I can plant the seeds right into the soil after germinating them?

Welcome,
You have a lot to read up on if you are serious about finishing this grow. As far as your soil, I have not used Black Magic but I would advise adding a lot of perlite to the soil so that it drains well.

Yes, you can plant the seeds after they germinate or terminate them directly in soil.

This is a good place to start....ten steps to growing cannabis. It includes recommendations for nutrients.
http://www.growweedeasy.com/simplest-guide-to-growing-cannabis

no need to go elsewhere, the info is here
https://www.rollitup.org/t/how-to-grow-marijuana.937/

outdoor grow, 18in pot i use 4 parts premium potting mix, 2 parts commercial compost, 1 part coarse river sand for drainage,1.5 level garden trowels b&bone, .5 scoop of gypsum, 2 generous handfulls of slow release fertiliser, a dash of trace elements. mix thoroughly and transplant well established seedlings. i water using tank water [no fluoride] and once every 4-5 days feed with fish emulsion. mine grow [just saying] [4 ww fem, 2 cal skunk] so sturdily its fkn awesome. no doubt there are amillion stories in the big city, this is just one.lol.