I don't understand the bellow two sentences' meaning

I don’t understand the below two sentences meaning :

**PAC mode**: All http/socks data is forwarded through the proxy server. 
Only software that supports socks5 or uses system proxy can use Shadowsocks (general browsers use system proxy by default).

**Global mode**: does not require the application to follow a specific operating system platform, 
but simply passes the packet without caring about the application protocol (such as FTP, HTTP, and NNTP requests).

PAC mode only work for browsers and applications that can be configured to use the proxy. Global mode send all requests from all applications.