I have a word2vec embedding - now what?
First, make sure, you have the same vocabulary in your word2file and in your Keras code. If you Keras Tokenizer, you can simply call fit_on_texts with the text actually being the vocabulary.

Load your word embeddings as numpy matrix (just read all the numbers and then call np.array).

When creating the Embedding layer, call set_weights and set the loaded matrix and set trainable to False.

You can find more at Keras blog but I am not sure how up to date it is because it is from 2016.