How datacenter proxies work
Your software sends each request to the proxy server first. The proxy forwards it from its own IPv4 address, receives the reply and passes it back. The website only sees the proxy's address and the country it is registered in.
Because the address belongs to a hosting company rather than a home connection, it is fast and stable, but websites can tell it is a server address. That is fine for most research, testing and automation of your own systems; if you specifically need a home or mobile connection, see residential or mobile proxies.
Private or shared: what changes
A private IPv4 proxy (called HQ proxy in the shop) is used only by you during the rental. Nobody else's traffic goes through it, so its reputation depends only on how you use it.
A shared IPv4 proxy is given to up to three customers at once. It costs a fraction of a private IP, but other users' activity affects the same address.
An IPv4 mix pack is a batch of private IPs spread across the countries of one regional package, delivered as a single list with separate HTTP and SOCKS5 ports for each proxy.
Connecting to your proxy
Private and shared IPv4 proxies are delivered as host:port:login:password, and the one port accepts both HTTP/HTTPS and SOCKS5. Mix-pack proxies come with one HTTP port and one SOCKS5 port per address. See the SOCKS5 and HTTP setup guide for examples.