connection pooling in java better way

Question

I am working on DB connection pooling. I can see various options to create connection pool using Application server side and then looking through JNDI, hibernate connection pooling where I can set properties in configuration file.

I have 2 questions.

1. I have set properties as below

   hibernate.c3p0.max_size=20  (Max number of database connections to open)
   

   what will happen if there are 100 users accessing my website and I have specified only 20 connection objects. Will remaining 80 users will be waiting till 20 users are done with their transaction OR how remaining 80 users can connect to application?

2. which is better way of connection pooling using hibernate configuration or through Application server side ?

Thanks in advance.