You are asking several questions here. Your subject header says "starting from selection". You can easily do that; check your key command assignment for "start from selection". It will do as it suggests; start playback from the beginning of the selected region.
Then you asked about locators and how to set the beginning and end of the selection. If you mean setting the start and end point of the locators, there are several ways to do it. You can set them based on selected region or marker boundaries, or you can set the left and right points individually either by key command, in the transport, or by dragging the ends of the green cycle bar in the bar ruler.
But setting beginnings and ends of selections is something else; you can use key commands for tabbing to region boundaries or transients while extending the selection. The marquee tool is useful for this. There are several key commands for manipulating marquee selection boundaries. And you can also use marquee boundaries to establish playback ranges. Logic's transport will stop and start at marquee selection boundaries.
And then you asked how to go back to the default where ti plays from beginning to end. Presumably by "beginning' you mean bar 1. Take off cycle mode and disabel any marquee selections; then use the regular rewind to beginning key command or double hit the stop key command to go back to the beginning.