The sentence that uses the imperative mood is:
"First, put the eggs in a separate dish and beat them."
The imperative mood is used to make suggestions or requests, to give orders, advice or instructions.
In this case, it refers to a recipe, so it is regarding instructions.
When using the imperative mood, the verb is not preceded by the particle "to". For example: "put the eggs in a separate dish."
To make it more polite, the imperative mood can be used with the word please, especially when it is about a request. For example: "Open the window, please." Or: "Please, don't smoke here."