What Is Reserving A Name?
Reserving a name makes it so no one else can use that name in-game. For instance, if your name was "John Doe" and you put that EXACT name into your reserved name slot, no one except for you (or anyone using your account that you reserved it on to play defly) can use that name. People can still use similar names, such as "JohnDoe", or "John doe", but no one can use your name with those exact characters.
How Do I Reserve A Name?
First, you need to have premium. You then need to go to My Account and go to where it says Reserved Nickname. Put in whatever you want your reserved name to be. If that name is already reserved, an error message will show up and you will have to select another one. An easy fix to your name already being reserved is putting in and/or removing capitalization, punctuation, slightly different spelling, and ASCII characters (more on those later). After you choose your name, click the update button. There you go! As long as you did everything right, no one will be able to use your name!
What is Premium?
Premium is a paid service that allows you to do things like go ad-free. The advantages of Premium are a Discord VIP Role, no ads in-between deaths, a reserved nickname, a special badge that you can use in-game to show your support, and a free selection of a special category of skins. Premium costs $5 (Dollars - U.S), or 5€ (Euros - Majority Of Europe). I won't go too in-depth, because there is a whole article about it (here).
What are ASCII characters, how do I use them, and how do they work with reserving your name? (Had a discussion with Serial about this and he briefed me and added a notice in-game.)
ASCII characters are special characters that look different from normal letters/are symbols like the greek alphabet and the pi symbol. Such as, ≈, 𝔸, 𝞨, ☺︎, ⟪, ⟫, and ☞. FYI: SOME ASCII CHARACTERS TAKE UP MORE THAN ONE CHARACTER, SO YOU MAY NEED A SHORTENED NAME. These all can be inputted into the reserved nickname section, and you can use them. However, there is a process that makes these things hard to put into a name. I would suggest only using things like ☞ and 𝔸, to not confuse anything in the reserving process. To use ASCII characters on Windows, press alt + a series of numbers. These series' can be confusing, so I would suggest looking up a list of number combinations for common ASCII characters. On Mac, scroll over to your top-right menu bar, and go to keyboard settings. Then, select Show Emoji & Symbols and select your ASCII there. I will add other methods later, but you can always copy and paste. Once you know what your ASCII characters are, you need to input them into the reserved box. But wait, you can't input them as they are, you need to convert them to normal text. FYI 2: WHEN INPUTTING ASCII CHARACTERS IN NORMAL TEXT FORM, IT PREVENTS ALL ASCII CHARACTERS IN THAT COMBINATION OR LETTERS BEING USED. Prefer ASCII characters as any variant will be protected, for instance, A will reserve Ａ,𝒜,𝓐,𝔸... For instance, 𝕁𝕠𝕙𝕟 will need to be converted into John. J𝕠𝕙n will be converted into John still. Latin Characters such as æ, should still be written as æ. Symbols rather than symbol letters should be written as normal as well. ⁌⁃⁍ Should still be written as ⁌⁃⁍ when reserving.