How to configure port for external access?

Question

I need to access software from another machine in PORT 3000, but I can not do it for the IP of the machine, only by localhost.

erick@erickmordecai:~$ ifconfig
enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        inet 192.168.0.103  netmask 255.255.255.0  broadcast 192.168.0.255 
        inet6 fe80::4367:b9ff:87bb:2c8c  prefixlen 64  scopeid 0x20<link> 
        ether 38:2c:4a:8c:a3:33  txqueuelen 1000  (Ethernet) 
        RX packets 147266  bytes 200775157 (200.7 MB) 
        RX errors 0  dropped 0  overruns 0 frame 0 
        TX packets 76656 bytes 7752958 (7.7 MB) 
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0 
        inet6 ::1  prefixlen 128  scopeid 00x10<host> 
        loop  txqueuelen 1000  (Loopback Local), 
        RX packets 17420  bytes 4937968 (4.9 MB) 
        RX errors 0  dropped 0  overruns 0  frame 0 
        TX packets 17420  bytes 4937968 (4.9 MB) 
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

erick@erickmordecai:-$ nmap localhost

Starting Nmap 7.60 ( https://nmap.org ) at 2018-10-05 22:47 -03 
Nmap scan report for localhost (127.0.0.1) 
Host is up (0.000045s latency). 
Not shown: 997 closed ports 
PORT     STATE SERVICE 
80/tcp   open  http
631/tcp  open  ipp 
3000/tcp open  ppp

Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds 

erick@erickmordecai:~$ nmap 192.168.103

Starting Nmap 7.60 ( https://nmap.org ) at 2018-10-05 22:47 -03 
Nmap scan report for 192.168.103 (192.168.0.103) 
Host is up (0.000051s latency).
rDNS record for 192.168.0.103: erickmordecai
Not shown: 999 closed ports 
PORT   STATE SERVICE 
80/tcp open  http

Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds erick@erickmordecai:~$

I did not understand why I have some open ports for localhost, and others for the IP of the machine on the network.