While there are a number of good virtual tabletops (VTTs) designed specifically for playing RPGs—I have had good experiences playing in a campaign on Foundry, and have read recommendations for Fantasy Grounds—I admit that I am a bit of a curmudgeon when it comes to mixing technology with gaming. The Covid-19 pandemic has made it a bad idea to play together in person, however, and one can only hold out for so long while waiting for the vaccine. For that reason, and because I wanted to playtest my scenario for this year's Con of the North, I decided to try a session using Google as my platform. Here is now I did it.
The first step is to open your Google Drive and create a new folder for that session. This helps to keep everything organized.
After that, upload into that folder any files that you want to share with the players. I recommend quick rule reference sheets, pre-generated characters if you're using them, handouts with background information, notes from previous sessions, and the like.
Create a link to share this folder with your players.
Next, create a Google Drawing in that shared folder. This will be your battle map.
In that drawing, upload the map that you want to use for the opening encounter (Insert > Image > Upload from computer).
Be sure to set that map as the background for this Google Drawing (right-click > Order > Send to back.) This makes sure that the map doesn't cover up character markers.
You can create character markers using cropped images of the heroes and NPCs. Add them to the Google Drawing just like you did with the map; you'll probably need to resize them to fit.
This sets up a battle map that you as the GM control. If you want to let the players move their own heroes on the map, then you just need to change the sharing settings for the Google Drawing (Share > Change > Anyone with the link).
You can add clues to the shared folder as you go.
Finally, you can add features to the battle map, too, as the heroes discover them.