Learn German: Bei einer Grippe hilft nur Ruhe. - With the flu only rest helps.

In German, mit is mainly used for tools (like writing with a pen) or accompanying people (like going with a friend). When talking about situations, conditions, or illnesses (meaning "in the case of" or "when you have"), you use bei.

Why is the verb hilft placed before the subject nur Ruhe?

This happens because of the V2 rule, which states the verb must be in the second position of a main clause. The phrase Bei einer Grippe takes up the entire first position, so the verb hilft must come next. This pushes the subject nur Ruhe (only rest) to the third position.

Why is it einer Grippe instead of eine Grippe?

The preposition bei always forces the following noun into the dative case. Since the word for flu is a feminine noun (die Grippe), the article eine changes to its dative form, einer.

Does Grippe mean the same thing as a regular cold?

No, die Grippe specifically means "the flu" (influenza). If you want to talk about having a common cold, you would use the word die Erkältung.