CB blew when trying to measure the current using multi meter. What went wrong?
Current is aways measured in series with something.

An ampere meter "looks" like a short circuit.  It works by measuring the voltage across a (very) small value resistor. Like, far less than 1ohm.

Assume your meter is using a 1 ohm current sense resistor, then at 120VAC it would draw 120A and "look" like a short circuit to your circuit breaker (which is rated for probably around 15A.)

If you are lucky, you only blew a fuse in your meter and damaged the cables.  You may also have destroyed the meter completely.

The sparks may also have damaged the contacts in the outlet.



The way you had it connected the first time was for measuring voltage.

With the selector set to measure current but the cables connected for measuring voltage, all you got was non-sense - 3.5A is unrealistic for short circuit current from an outlet, and 3.5V wouldn't make much sense on a 120VAC outlet.