DIAGNOSIS: The interface changed with firmware updates. The 'Virtual Server' feature is still there, but it's now under a section called 'NAT Forwarding'.
FIX: Here's the step-by-step. 1) Log into the router's web interface at tplinkwifi.net. 2) Go to the 'Advanced' tab at the top. 3) In the left sidebar, look for 'NAT Forwarding'. Click it to expand. 4) You'll see 'Virtual Servers' right there. Click it. 5) Click 'Add'. Now you need three key pieces of info: the 'Service Port' (the port you want open, like 25565 for Minecraft), the 'Internal Port' (usually the same), the 'IP Address' (the local IP of the computer or console on your network that will receive the traffic), and the 'Protocol' (usually 'ALL' or 'TCP&UDP'). Fill those in, save, and you're done.
IF THAT DIDN'T WORK: First, make sure the device you're forwarding to has a static IP address on your local network. If its IP changes, the port forward breaks. You can set a 'DHCP Reservation' for it in the router under Advanced > Network > DHCP Server.
HEADS UP: Port forwarding opens a door in your router's firewall. Only forward ports you absolutely need for a specific game or application. Also, your ISP might block common service ports (like 80 for web servers) on residential plans, so if a forward isn't working, that could be why.