There are many reasons why you may be looking for online sheet music
You may find some free online sheet music if you look around, but your selection will be limited. Some of this stuff will be accurate, but you have to watch out for parts that may not sound right. Some that put this online have the best of intentions, but they may have tried to transcribe it on their own, and there can be mistakes. Usually these mistakes on online sheet music are minor, but can make a huge difference in the music. Luckily, most people can find and fix the mistakes on their own.
Other online sheet music is going to come with a price tag, but when you buy this way, you are usually getting sheet music that is very accurate, and you know it have come from a legal source. If you aren’t sure if the online sheet music you have is legal, search around for the copyright. Remember that even when you buy a set, you may have to pay money to make copies of it. When you are getting online sheet music for use in a band, at a school for example, you have to pay attention to the specifics of what you can do with it and what you cannot.
You may also find online sheet music in a different form. This can be program that can help you get your own sheet music for stuff you wrote on your own, or a song you are trying to figure out so you can play it. You can add your own notes and such to the program and it will attempt to print out the proper sheet music for you. This is exceptionally useful if you write your own music, and you want to write out parts for the rest of your band.