Acting is a great hobby. A lot of people look for audition opportunities at their community theater. Most cities of any size have from one to five community theaters that rely on local talent. It doesn't pay in money but in experience. It also pays dividends in friends while you gain valuable training. Some community theaters offer inexpensive classes for beginning actors. Local universities often offer theater classes as part of their continuing education program. These courses are also inexpensive and taught by a drama professor.
As you seek roles in theater, it is important to remember a common adage: There are no small parts, only small actors. Starting in small roles does not mean that you will be stuck in small roles forever. You are gaining training that you can later translate into larger roles.
Live theater requires that you speak loudly. It also requires that if you are on stage, you remain in character. Memorization of your lines and your blocking is also important. Blocking refers to the stage directions that the director gives your character. At auditions, remember to dress neatly and be ready for a 'cold read'. If you aren't good at reading on the first try, ask for time to review the material. If you are told to bring a monologue, you can try the theater section of the library to find an appropriate one. Choose a monologue that fits your personality and is easy for you to understand and memorize. Each page takes about a minute. Usually two minutes is what directors ask for. So practice your piece, memorize it and be prepared to goof up. Think about what you'll do if you make a mistake. A director cares much more about how you handle yourself than perfect memorization.
If you are interested in screen acting, there are other considerations. Unfortunately, many agents charge you money and do very little actual representation. If you think you have that 'special something' for the screen, start small. Have professional photos made, but don't go into debt. Share the photos with an agent but refuse to pay for representation. A true agent finds you paying jobs. They only take money as a percentage of the work they get for you. Watch local websites for chances to be extras in movies or casting calls for local commercials. Most actors don't make big money. So don't look at acting as the train to success. It's much more fun to look at it as a chance to shine and to enjoy life.