confusion surrounding headers and header guards

so im trying to write programs in multiple files however if i include header files more than once it'll cause an error but if i make header guards if the file has already been included it wont be included again which would cause the things i need from my headers to not be included, can anyone try to explain how i should handle this or send github repos to small projects that show how you should handle this

https://redd.it/1tzd5hg
@r_cpp