Show date on the Apple Watch Series 2 Home screen
Apple Watch doesn't have a great variety of faces to choose from. You have to choose one that has a "complication", which means configuration option and/or display option, that can be configured to display the date. Press and hold your current face at a location that doesn't activate another function, swipe left and right to look at available faces, then choose the customize button at the bottom or the New choice, and select one that includes date by default or lets you add one thru the use of a complication. You can control this process with greater intricacy using the Apple Watch app on iPhone.