but I cannot find how to set an end point so playback stops there or loops when it gets there.
you mean the workarea:
you can either drag it manually or use B and N shortcuts for Beginning and eNd
Welcome to Ae I would suggest you learn it from the ground up and not by intuition. this will make sure you have a good knowledge base. many users rush to the fun stuff and that's understood, but you can only go so far before you get stuck. if you want to really know Ae and enjoy it, you have to know the basics first. there are many good ways to start: After Effects CC tutorials | Learn how to use After Effects CC and I would also recommend learning from a well constructed built in essnetial courses in Ae. Lynda has some great ones.
Argg...someone shoot me, please. This is the right answer from testing it just now. I'd swear I had already tried sliding those around since they're exactly where I'd expect something like this to be, but I guess I'd tried it wrong some how. I'm still a bit confused by the similar smaller markers right above them (same color) that also slide back and forth, but I'll catch on soon enough. I agree about the tutorials, and I have several I'm working through but still have a way to go.
Anyway, thanks very much..and the 'B' and 'N' keys are helpful too.
I'm still a bit confused by the similar smaller markers right above them (same color) that also slide back and forth,
yes, this can be confusing. this is the time navigator bar - you can use the sliders to specify precisely a range of the timeline you want visible, you can then move that range around. I personally don't use it much in the timeline panel since there are other shortcuts that are more efficient for me to navigate in my timeline. the time navigator bar is more helpful for me in the footage/layer panels - but pace yourself, you will get there soon enough.
BTW hover over almost any switch in Ae and you will get a pop up information about it