What these MySQL global variables really mean?

Today I contacted a hosting company to get information about their Java hosting performance. In their response, they said

MySQL:
max_connections=300
max_user_connections=50

Apache:
MaxClients 150 (this mean that 150 query could be handling at once, all other queries will be put to the queue).

Now I am confused. I read the NySQL developer document seeking for an answer but I am not convinced enough. Here are my questions;

1. What is the difference between max_connections and max_user_connections ?
2. Does it mean only 300 people can use the site at once? Or only 50 people? or something else?

The application I have is an online HR package, where users and their sub users will log into and perform operations like insert, delete, update. Any help would be greatly appreciated.