Prayer is a conversation with God. It is listening and speaking. It is being quiet and saying something. It is an "address to God in word or thought" (Merriam-Webster). It is adoration and confession and thanksgiving and supplication (ACTS). It is praise and repentance and adoration and yielding (PRAY).
But perhaps prayer is mostly an invitation to begin or to develop a relationship with the God who made us and loves us.
Do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. Philippians 4:6