''A browser is not a network diagnostics tool!''
Open terminal: in /Applications/Utilities/Terminal.app
Does the computer have an IP Address?
ifconfig
If the IP address is in the form 169.254.x.y, address assignment via DHCP usually does not work.
Routing
Does the computer have a route out of the local network ?
check routing: netstat -rn
the output of the route(s) should contain a so called 'default route' or 'default gateway':
If an IP address is configured and a default route exists, the network should actually work.
If not:
can the default gateway be reached ?
ping IP.ADDRESS.FROM.GATEWAY
does the name resolution via DNS works?
does the name resolution via DNS work ?dig at www.heise.de
; <<>> DiG 9.10.3-P4-Ubuntu <<>> www.heise.de a;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20883
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.heise.de. IN A
;; ANSWER SECTION:
www.heise.de. 582 IN A 13.14.15.16 <- IP-ADDRESS-HERE
;; Query time: 0 msec
;; SERVER: 127.0.1.1#53(127.0.1.1)
;; WHEN: Wed Feb 21 14:10:23 CET 2018
;; MSG SIZE rcvd: 46
if an IP address and not SERVFAIL is shown, you can assume that the name resolution works too.
now finally a browser can be used for testing, if a page is already open, please reload it with SHIFT-Reload (mostly F5).