Hi @Archenth2001,
Welcome to the forum, the first think you need to is read the Manjaro Guide in order to install it properly. You are also not the first one who make in troubles trying to install Manjaro. For example, read this post in order to see whether you follow the installation guide.
‘Questions about dual booting Windows after installing Manjaro’
The other problem could be related to this post:
‘Os-prober, and grub can't find windows 10’
Hope this help, regards