You'd have to give some more information. How do want to connect to the Internet? Via Ethernet port (wire) connected to your modem/router? Or wireless?
If you're on a wired connection using a modem (NOT router), what are the requirements from your ISP?
To check if you have some DNS problem, try the following:
Open a terminal window and enter the following command:
It should give you something like that:
PING 18.104.22.168 (22.214.171.124) 56(84) bytes of data.
64 bytes from 126.96.36.199: icmp_req=1 ttl=42 time=77.2 ms
64 bytes from 188.8.131.52: icmp_req=2 ttl=42 time=78.4 ms
64 bytes from 184.108.40.206: icmp_req=3 ttl=42 time=76.4 ms
64 bytes from 220.127.116.11: icmp_req=4 ttl=42 time=77.1 ms
64 bytes from 18.104.22.168: icmp_req=5 ttl=42 time=75.8 ms
64 bytes from 22.214.171.124: icmp_req=6 ttl=42 time=76.3 ms
--- 126.96.36.199 ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5007ms
rtt min/avg/max/mdev = 75.846/76.910/78.425/0.873 ms
If you get the above (packets transmitted, packets received, and 0% packet loss) then you have a connection to the Internet but your DNS entries aren't set up or set up incorrectly. Check your network settings for DNS entry. Normally setting it to DHCP is all that needs to be done. If not, you can manually enter the DNS (188.8.131.52 is actually a DNS server, so you could enter that).
Of course this is just a wild guess. The best is to share your setup and check for the requirements of your ISP.