Step-by-step explanation:
There are several methods to identify and categorize objects in space but the 3 important are:
•Mass/Size
•Revolution
•Gravity
Example:
If you look at the planet Mars you will identify it by many methods but the basic way to indentify it is by looking at it's gravitational pull, Mass and size of the planet and the revolution of the planet around the star.
You can also identify them by looking at their elements present in it (like mars is red due to presence of high amount of iron/red soil in it), and Like Saturn is mostly identified by it's rings. It's not always about planets but it's also about the asteroids, stars, Natural satterlites of planets (like moon) and more.
Hope this helps you
Have a nice day :)