How to config the LAN interface users to Internet (Basic configuration)

[coachever]

I think the problem is on DNS Resolver, which is, when I uncheck the DNS Resolver

then the client can connect to the internet. On the other hand, when I check (enable) the DNS Resolver

clients then unable to connect to the internet. So the problem is DNS Resolver, i guess. What should I do?

[Gertjan]

The Resolver should be activated, or the Forwarder.
One or the other.
Both : impossible.

Up to you to choose one.
However : The Resolver (or Forwarder) has to be set up correctly.
When you installed pfSense, the Resolver is activated and will work right out of the box. No changes from you are needed.

Running pfSense with no Resolver neither Forwarder is no advised at all.

And what about answering questions ?
Like the one @JeGr asked ?