If you are trying to record audio from your synth, find the audio outputs on the synth and connect them to your soundcard audio input. In Mixcraft, select that input as your source. Then press record to record the sound.
Hope this helps.
Mixcraft8RS(418)64Bit, Win. 10 64Bit, Intel i5 @ 3.20GHz, ssd 250GB(os),1TB hdd(library audio),1TB hdd (recorded audio),Nvidia GeForce1050i video,16GB RAM,Focusrite 18I20 2nd gen usb,Motu 5 ch.midi interface, D5,U220,Keystation88,B4000+,Leslie,Rhodes73mk1