OpenStreetMap Canada

I recommend starting with StreetComplete. It's a lot of fun.

For desktop, start with the standard ID editor which is user friendly.

Start with easy stuff if you feel overwhelmed: POIs like bike racks, garbage bins, benches, etc.

You can create simple buildings with relative ease in the standard editor, or you can use something like Rapid to make things easier. You don't have to worry about getting all the details entered for every POI or building, as long as it's accurately on the map, another user will likely fill in the blanks.

There are a ton of apps to make editing easier, including OSM Go!, Streetcomplete, Every Door, etc. Some are better at specific tasks, like adding details/addresses to buildings, while I find that others are great for adding quick POIs on the go.

On desktop, I stick mostly to Rapid or the OSM editor. I've never used an actual Windows editor, as I'm sure they have a steeper learning curve. Start with easy and work your way up :)