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.
I hate to sound anal, but if you're just starting out with Logic; you should start off on the right foot. Selection is the wrong term to be using. What are you are doing isn't really "selecting". You are setting the left and right locators and establishing a cycle range. You can then make selections based on the cycle range or locators if you want to. Or you can establish selections that have nothing to do with the locators or cycle. What you are doing technically isn't a selection.
I am only pointing this out because using the right "language" is so important at the beginning when you are trying to figure things out by looking for them in the manual. or even when posting questions on forums.
Again, I'm not trying to be critical; just helpful (I hope!) Knowing the right way to search the manual is half the battle with this (or any) DAW.