Evolutionary algorithm - how to select the parents
As a simple method, you can use the roulette wheel selection. The idea is that every individual has a chance to be selected as a parent, but the more fit an individual is, the more likely it is to be selected. Let $f_i$ be the fitness of the individual $i$. The probability $p_i$ of choosing $i$ as a parent for the next round is $p_i = f_i / \sum_{j=1}^{N}$, where N is the size of your population.

Here's an example in the context of TSP. For simplicity, let's say your population is only 4 individuals. Assume every individual is a tour of some length. The shorter the tour, the higher the fitness. Let the fitness values of the tours be $F = \{ 25,15,10,5 \}$. The sum of elements is 55. We divide every element $f_i$ with 55, and obtain $\{ 0.45, 0.27, 0.18, 0.09\}$. To implement the roulette wheel, you can use a weighted random generator if the language provides one (if not, just roll your own).

If you want to experiment with other genetic selection operators, look up other more complicated selection methods. To get you started on those, have a look at selection operators.