What kind of exercise to start with if I haven't really been active for several months?

Haven’t done any exercise in months, but I used to be very active. Now I get tired easily when I attempt to exercise, especially if I do too much strenuous exercise, I feel like I might pass out! On the other hand, light exercise has been discouraging because I feel like I’m wasting my time. Therefore I haven’t been able to keep up with a consistent fitness routine.
I’m not overweight, just feeling out of shape.

What are some exercise routines to start with to build my energy back up and get toned again, without overdoing it?