Trying to solder, leaving goo instead of solder

6-pin USB C is recommended to solder using hot air fan if possible. You have to pre-solder the connector pins from bottom, clean the motherboard using wick (goot wick), add flux to the connector pins. Pre-heat the board using hot air fan and then apply a socket. gently pushing it from the top. Hot air fan should blow from the bottom to avoid socket damaging.

There also another methods, like using soldering paste etc.
Of course, you can do it using iron, but you have to take very thin copper tip and good, well heated soldering station.

Things like on your photo always happens with a beginner. Plastic near the socket is melting. It's impossible to solder it, plastic will ruin the solder because it contains carbon trash and acids.