Potentiometer position with op-amp
If your ADC can handle source impedance of 2.5K ohms (maximum) you can directly use the pot. 

The op-amp can be used as a buffer to minimize variations due to the (typically large) tolerance of the pot element. 







simulate this circuit &ndash; Schematic created using CircuitLab

If it cannot handle 2.5K then you can add an op-amp voltage follower. In both cases the op-amp needs to be able to operate from 3.3V and in the second case the output needs to be able to swing near ground and the input common mode range include ground (single-supply or rail-to-rail input and output).