需要htaccess知识

I've put on htaccess on xamp (I've used it before)

but trying to change the following

index.php?admin&user&list

to

example.com/admin/user/list

I have a few other pages behind /admin/. Do I need to make 1 for every page?

You can try:

RewriteEngine On

RewriteCond %{THE_REQUEST} \ /+index\.php\?
RewriteCond %{QUERY_STRING} ^(.*)&(.*)$
RewriteRule ^index\.php$ /index.php?%1/%2 [L,NE]

RewriteCond %{THE_REQUEST} \ /+index\.php\?
RewriteCond %{QUERY_STRING} !&
RewriteRule ^index\.php$ /%{QUERY_STRING}? [L]

This makes it so when you request http://example.com/index?abc&def&ghi, the rules will internally route the request to /abc/def/ghi