Audacity is not good for Recording Skype. It is difficult to get both sides of the conversation at similar volumes. Specialist Skype recording programs (such as Pamela) work a lot better for recording Skype.
The Behringer UCA 202 is a decent little USB sound card but it is designed specifically for recording “line level” signals (such as the output of a mixing desk). There are a couple of reviews of it in this thread: https://forum.audacityteam.org/t/sound-card-reviews/8375/1
Stereo Mix with the UCA 202 usually (depending on the Operating System) requires using a stereo audio lead to connect the output to the input (and use the headphone socket for monitoring).
The USB Samson microphone does not require any additional sound card - it plugs directly into a USB socket of the computer.
Audacity can only record from one audio device at a time.