HOSTAPD & DNSMASQ Hotspot Port forwarding my PC

Question

I have a raspberry pi 3 and I'm currently using it as a internet hotspot: I use a ethernet cable to get the connection, and the WiFi card to share it. (Eth0 --> Wlan0). The only problem with this is that I can't do any port forwarding with the devices connected to it... I have searched for many hours with no successful results, I tried 'iptables' (which i'm not familiar with...) with still no success...
So here are some infos that might help: (ifconfig on the raspberry pi)

pi@raspberrypi:~ $ ifconfig
eth0      Link encap:Ethernet  HWaddr b8:27:eb:1b:c6:ec  
          inet addr:192.168.0.37  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: 2a01:e35:2f32:7120:ba27:ebff:fe1b:c6ec/64 Scope:Global
          inet6 addr: fe80::ba27:ebff:fe1b:c6ec/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:789 errors:0 dropped:1 overruns:0 frame:0
          TX packets:344 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:73638 (71.9 KiB)  TX bytes:43983 (42.9 KiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:180 errors:0 dropped:0 overruns:0 frame:0
          TX packets:180 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:12958 (12.6 KiB)  TX bytes:12958 (12.6 KiB)

wlan0     Link encap:Ethernet  HWaddr b8:27:eb:4e:93:b9  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:13 errors:0 dropped:13 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2775 (2.7 KiB)  TX bytes:0 (0.0 B)  

And 'ifconfig' on my PC:

nuf@nufPC ~ $ ifconfig
enp4s0f2  Link encap:Ethernet  HWaddr 74:d0:2b:ba:93:db  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:1552790 errors:0 dropped:0 overruns:0 frame:0
          TX packets:880671 errors:0 dropped:7 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1836089487 (1.8 GB)  TX bytes:99384524 (99.3 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:1279658 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1279658 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:88890909 (88.8 MB)  TX bytes:88890909 (88.8 MB)

wlp3s0    Link encap:Ethernet  HWaddr 24:fd:52:3c:f6:ee  
          inet addr:10.0.0.17  Bcast:10.0.0.255  Mask:255.255.255.0
          inet6 addr: fe80::675:363e:5f61:f10c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:71245 errors:0 dropped:0 overruns:0 frame:0
          TX packets:49945 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:76745606 (76.7 MB)  TX bytes:7135427 (7.1 MB)  

So for exemple I would like to create a server which use the port 1337 I can't directly forward it to my box, I need to forward it to my Raspberry which forward it to my box I guess... I hope you can help me :)

Answer 1

I have used:

iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain
iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE
iptables --append FORWARD --in-interface wlan0 -j ACCEPT

iptables -t nat -A PREROUTING -p tcp -m tcp --dport (PORT NUMBER) -j DNAT --to-destination (COMPUTER IP CONNECTED TO PI)
iptables -t nat -A POSTROUTING -d (COMPUTER IP CONNECTED TO PI) -p tcp -m tcp --dport (PORT NUMBER) -j MASQUERADE