Locks everywhere is a good start to understand how SQL Server provides logical consistency. Every operation has a lock and latch.
What does Latch mean? Latch protects memory on Buffer Pool, is a method that provides physical consistency.
SQL Server does operations in memory, that means, it read the page from disk and put that page on buffer pool to work there. If someone tries to update the data, the page is changed in memory and SQL Server writes the change in the transaction log file. (More about logging)
Basically, Latches are physical locks and hold the lock only for the duration of the physical operation, while the Locks are logical and maintain the lock until the transaction finishes. Both types guarantee data consistency.