grammar - Usage of "do not " vs "does not"

I am trying to understand the grammar behind using "do not" vs "does not".

Consider the following sentences.

1a. The way items are added to the cart does not guarantee an order. vs

1b. The way items are added to the cart do not guarantee an order.

2a. We will skip the entries that do not match vs

2b. We will skip the entries that does not match