You don't "have" to take it at all -- it's your choice. You don't describe anxiety, though you may have it, you describe some physiological symptoms. Do you feel anxious? Do you suffer insomnia (though benzos are a problematic way to treat insomnia, this drug is used for that)? If you don't feel anxious for no reason, then this doctors may be ascribing this to anxiety when he or she just can't or won't find the reason for it. But if it is anxiety and it's not crippling your life, you can and probably should try talk therapy first to see if you can solve the problem without medication. If it isn't anxiety you need a new doctor or a specialist or someone who might be able to diagnose what's going on. Take as needed means when you absolutely have to do something and can't because of your anxiety -- fear, in other words -- and at other times learn relaxation techniques or take something longer lasting in relief such as an antidepressant that works all the time. But again, no drug is problem free, so if you can try to solve it without medication that's great. If you can't, then there is medication. But it is up to you. As for the use of this drug, I don't think many people on this forum will have used it as it's not used much if at all in the US -- it's mostly used in Australia at this point. But most of us have taken other benzos, and they can be hard to stop taking if you take them every day. Just the way it is, so you only do that if you must. But it's your decision.
I don't understand "take when need" because my symptoms lasts throughout the day, and how long do I have to keep taking this pill?
If you only take it as needed rather than regularly you are less likely to become addicted to it, as is true with all benzos.