I assume that you digital meter has three test lead jacks. Right?
1: Positive
2: Negative
3: Amps

To measure current, put the positive lead in the Amps jack and the negative lead in the Ground jack.

Set the meter to your highest reading for DC Amps.

(Do NOT use undersized wiring for these connections, especially beware of alligator style jumper wires. You need to make solid connections with the proper sized wire!)

Connect the three negative solar panel leads to the negative solar panel terminal on the charger.

Connect the three positive solar panel leads together to form a termination point.

Connect the Positive lead to the termination point of the three positive solar panel leads.

Connect the negative lead to the positive solar panel terminal on the charger.

[(3) + solar panel leads] [(3) - solar panel leads]
----------------------------| |--------------
----------------------------|----[+ meter -]---[+ charger-]----|--------------
----------------------------| |--------------

Does this make sense?