My question is about using a stage name.

My last name is long, nobody can pronounce it correctly, and to be truthful I don't care for it much. I am wondering if to use a stage name do I have to legally change my last name? If not do I have to explain to directors etc. that it's only a stage name? Thank you very much for your help.
You do not have to legally change you name. However, if you choose a stage name that a professional actor already has, you would not be able to use it if you ever hoped to join an actor union and get paid for your acting work. So choose carefully. You do not have to mention that you are using a stage name. However, if you get paid, you will have to make sure your checks are made out to whatever name you use for your bank accounts and that you don't run into mix-ups with social security and taxes. Talk to your bank about setting up your accounts to make that possible.