It's not about "deciding" to add a block. If you're mining, you are in a race with many other people to "add a block". This answer has more detail:
The transaction fees are calculated by the pool when they decide to add the transactions into a block they are trying to mine. The fees are not specified by a number tagged on to a transaction. It is actually the difference between the inputs and outputs, the unused amount of the inputs.
So the fees are in there when you find a block. As the mining computer (or pool), you get to keep the difference between inputs and outputs in the transactions which are in the block. You
can make decisions about which transactions to try to include in the block as you go looking for a block and receiving transaction broadcasts on the network.
About starting your own pool, you're going to be in tough competition. Since you're just learning the very basics here right now, it's doubtful that you're ready to compete with the big players out there. But nice enthusiasm tho!
Zetaray makes a very good point, and I've bolded it to add some emphasis. We constantly talk about including fees with our transactions, and that higher fees tend to lead to transactions being included in blocks sooner. The reality is that the fees are nothing more than the difference between the inputs and the outputs. For example, if I use two inputs of 1
BTC each and my output is only 1.05
BTC then I have generously given 0.95
BTC as a fee to whoever includes my transaction in a block. Unless you're creating your own raw transactions, that stuff is hidden from you. You just say, "Send XX BTC to some address and pay YY BTC as a fee for doing it."