SAT is a threshold, the simplified acquisition threshold.  You can use any of the simplified acquisition procedures (SAP) found in FAR part 13 if your action is expected to be at or below the SAT.  See the ability to use SAP for commercial items at FAR subpart 13.5.

The policy for SAP can be found at FAR 13.003.  Guidance for the different types of SAP (including micro-purchases) is found throughout FAR part 13. If you were below the micro-purchase threshold you could look through FAR subpart 13.2 and it will discuss use of the purchase card among other things. FAR subpart 13.3 has guidance and descriptions for additional simplified acquisition methods (e.g. the Purchase Order).

A good place to start to learn more would be to take DAU's CLC 005 - Simplified Acquisition Procedures.  It's a short-self paced module.