でWith, By (using)

で is a particle that has several different uses in Japanese. At its core, it is always used to highlight something that is 'required' to perform some sort of action/reach some kind of goal. One of these uses relates to 'things'. This comes across as 'by' or 'with' in English.

In these sentences, the item is considered essential for the action to be performed. While other items may be used, で simply highlights the one that was chosen.

で is also used when groups of people perform actions together, this is something that many people learning Japanese have trouble with initially (because と may also be used as 'with' for people). However, the use of で is actually the same as this by/with, meaning that the speaker considers the group as the tool used for performing the action.

The difference between と and で as 'with', is that で is used when everyone in the group has the same objective/end goal. と is used when each person is performing the action toward each other, not toward an external objective.