Tie between

The usual way is to enter the tie along with the note - you don't normally enter both notes then tie them. But if for whatever reason you've already entered the notes, just click the first then pres the tie button on the toolbar. To enter the tie normally, though, just hit the tie button while entering the notes. So, instead of clicking the half note icon then entering the half note, click the half icon then press the tie button. This enters the tie and the note at once.

Click below for my Quick Answer on how to enter ties:

Enter Ties

https://masteringmusescore.com/quick-answers/enter-ties