Hello! Playing with mods will only be possible if you have the Java version of Minecraft. If you have the Windows 10 version, mods are not compatible.
If you DO have the Java version, then I would suggest getting the twitch launcher, found at https://app.twitch.tv/download
This will prevent you from downloading mods from Bad Sites that contain broken/outdated/virused mods, and put everything in a nice package for you. After installing the launcher, just run it, and click where it says "Mods" near the top, then select Minecraft. From here, you will be able to browse packs made by other people, or create your own modpack by choosing the mods you want. Keep in mind when adding a bunch of mods, this can make the game run slower, and/or mixing mods sometimes they do not "play well" together. If you want a lot of mods, try adding a couple at a time, and trying the game to make sure it doesn't crash and is still playable. If you add a mod that breaks it, just go back and remove it.
I am not sure what you mean by "I want to change my person", but I would guess that it means you would like a new "skin" for your player. There are instructions on changing your skin in the Java edition here: https://help.mojang.com/customer/en/portal/articles/979200-minecraft-skins?b_id=5408
Instructions for changing your skin on the Windows 10 edition here: https://support.xbox.com/en-US/games/game-titles/custom-skins-minecraft-windows-10-edition
Hope this helps!
Good luck, and most of all have fun!