Here is the essential visor if you purchased the EOS100D + EF-S 18-55 IS STM. Besides its primary function to prevent sun glare on the lens, it helps protect the lens from impact. Very easy to place and remove. Concerning the correct positioning of the sun visor, a red dot is present on the target and another red dot is present on the sun visor. When the two are aligned, the sunshade is well positioned and can not be detached. Fast, easy.
I removed one star because the price is relatively high. This indispensable accessory should be part of the basic kit of DSLR but it would raise the price of the camera ... probably Marketing Strategy ...