If you're just getting started playing the guitar, there are three main accessories you should think about getting:
Protection comes in the form of hard cases, Bags, and Straps. A Hard case is best if you're going to be taking your guitar outside often, and don't want to risk any damage. if you're planning to gig look into hard cases. Soft bags are better for occasional trips but they're the easiest to carry. A guitar strap is so that you can stand up whilst playing your guitar without dropping it.
Strings come in heaps of different types. the most important thing to do is match the strings to your instrument. if you have an electric guitar, make sure you get electric guitar strings. Classical, make sure you get Nylon strings.
The numbers on strings define how thick the strings are. the smaller the first number, the thinner the strings. thinner strings are easier to play and afford more bending, with thicker strings having better tuning Hold and a darker tone than thinner strings.
The most common string size for electrics is 10-46 (10's), but it's all about personal preference. once you've decided, you should also make sure you have a tuner so that you can keep your new strings in tune.
Need help tuning? This guide will help you make sure your tuning correctly.