SingleStoreDB is a high-performance, real-time distributed SQL database that processes queries at lightning-fast speeds and can handle large volumes of data with ease. Writing efficient queries in SingleStoreDB requires understanding how to use shard keys, sort keys, indexes, limit the number of columns returned, and utilize aggregate functions. Tuning queries involves analyzing visual explains, using EXPLAIN statements, leveraging query plancache, partition configuration, and adjusting the partition to vCPU ratio to improve performance. By following these tips, users can write optimized queries and tune them for better performance, unlocking the full potential of SingleStoreDB.