Spanish often uses the singular with the definite article to talk about something in a general, category-wide way.
So El pie de gato mejora el agarre means a general truth: the climbing shoe improves grip.
English does this sometimes, but Spanish uses it more freely. You could also say:
Los pies de gato mejoran el agarre.
That sounds more explicitly plural, but the singular version is also natural as a general statement.
Because agarre is a masculine noun: el agarre.
Also, Spanish often uses the definite article with general or abstract nouns where English might use no article. So English may say simply grip, but Spanish naturally says el agarre in a sentence like this.
Here agarre means grip, traction, or purchase, depending on how you want to translate it. In the context of shoes or climbing, it refers to how well something holds onto a surface.