Lexapro is for a range of anxiety related problems like anxiety disorder, panic disorder, depression, OCD and more. Over about a months time, you will feel a lot better! However, it does not necessarily make you sleep better. If your anxiety gets better over time, your sleeping will too. But if you really have trouble sleeping, I take a low dose of Benadryl that my doctor said was perfectly fine to do. :)
It isn't a "sleeping pill" per se, although it can initially cause drowsiness, which many people find to be a bonus, if their anxiety has caused sleep disturbances. If you find it is causing drowsiness, make sure you are taking it at night. If your doctor ordered it to be taken in the morning, give him/her a call, and ok a change in dosing times to the evening. In the same respect, if you find it is making you a little more jittery (common) and your doctor prescribed your dose to be taken in the evening, call and ask for a change in timing to the morning,
Lexapro has helped countless people with anxiety. I was on it for years and it worked very well for me. Just be patient, changes don't happen overnight. Communicate any side effects to your doctor, if you experience them, they typically only last about the first 2 weeks of treatment, and then they will start to subside.
Good luck, let us know how it is going!