What steps do I have to take to buy/sell bitcoins? What's the minimum amount of bitcoins that I can buy, and how much will I pay for transaction in a buy/sell operation?
For a start and to get to know the different exchanges and wallets you should checkout: https://www.bestbitcoinexchange.io/ (I'm not affiliated with that website).
To buy and sell Bitcoin I recommend https://gemini.com and https://xcoins.io. https://coinbase.com is popular but I'm not a huge fan of them for a number of reasons.
Just sign up and add your bank account to purchase Bitcoin. Gemini allows you to buy/sell Ethereum as well.
If you're worried about adding your bank account I would use https://xcoins.io or https://localbitcoins.com
