The OPTIMIZE command is a SQL command that can be run regularly or Ad Hoc. What it does is pack small files into larger files. Additionally, you can specify predicates to only run the command on a subset of a table, and also specify that you want to ZORDER on specific columns of the table.
Auto Optimize is a table property that consists of two parts: Optimized Writes and Auto Compaction. Once enabled on a table, all writes to that table will be carried out according to the config. Optimized Writes lowers the number of files output per write, whereas Auto Compaction will perform a more selective version of the OPTIMIZE SQL command after each write, and will bin pack partitions that have a large number of small files per partition (50 small files at time of writing).
If you want to ZORDER a table, you must use the OPTIMIZE SQL command. Otherwise, you can follow guidelines for Auto Optimize found here