Go to Products then Manage Products
Click on the add bundle product button in the top right and you'll be taken to the create bundle product screen
Fill in all relevant fields on the Product Details tab and add images. Fields marked with a * are required. You don't need to put a quantity in because it will calculate the available quantity from the products you add to it later
Go to the Add Bundle Items tab on the top right, you don't need to worry about the Custom Fields tab or Sales Channels tab for now as they're both completely optional.
Now you can start to type your items in the box and the auto complete will find the item for you, you can add extra items by clicking the green add more button and remove them by clicking on the red bin icon.
Once your products are added the Available column will populate with the total stock of those products. The quantity column is how many of that product you want to use in the bundle above that the bundle quantity will generate how many total bundles you can sell. For example the bundle quantity below is 3 because we only have 3 of one of the stock
If you change the quantity then the bundle quantity will also update. For example the bundle quantity is 1 because it uses 2 of a product that we only have 3 of
Once you've filled in all the information you can save the bundle