The Differences Between Characters

I am new to this language so i have some questions to ask. What is the differences between ㅔe andㅐae, ㅓeo and ㅗ o? Aren't they are the same? Is there any pronounciation differences between them?

Also, How can ㄱ sound pronounced as 'k' in 카페? Isn't ㄱ was 'g'?

Lastly, what is the differences between chatacters normal versions and this (ㄲㄸㅃㅆㅉ) versions, aren't they are the same about the pronunciations?

Do you know any good website, playlist or smth like that for pronounciations, i really need some.

Thank you all in advance. Have a great, lovely day ❤️