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Coffee grounds can be used in many ways in a garden, including as fertilizer, mulch, and a slug and snail repellent:

Fertilizer: Coffee grounds are a good source of nutrients like nitrogen, potassium, and phosphorus that plants use for growth. They can also improve soil structure and increase micronutrients. Spread coffee grounds in a thin layer over the soil, rather than clumping them together. However, using too many coffee grounds around mature plants can stunt growth and suppress root development.

Mulch: Coffee grounds can help prevent soil from drying out, protect plant roots, and insulate plants. Cover the soil around the base of the plant with well-dried coffee grounds and water thoroughly.

Slug and snail repellent:  Caffeine in coffee grounds can repel slugs and snails. Spread the grounds around vulnerable plants to create a barrier.

They do not however lower soil ph.