Once you have some content pieces available, you can start building the menu.
Go to Appearance > Menus and create a menu (give it any name you wish, this is only visible to us). Click “Create Menu”.
Now, you’ll be given the option to chose a Display location for the menu. Check “left top menu” to get started.
To add items to the menu, look to the various blocks under “Add menu items”. Your pages (About, Blog, Events/Calendar) can be added by placing a check in the box next to each, then click “Add to Menu”. Same with Categories.
Once all is added, click “Save Menu” and you’re done.
Need more info? Try here: https://wordpress.org/support/category/basic-usage/