Just for the sake of pedantic accuracy, the process is as follows:
2/3 of both houses of Congress approve an amendment;
A Constitutional Convention is called which then proposes amendments.
After one of those two things has occurred, 3/4 of the states must ratify the proposed amendment.
I say this mainly to combat the myth that a constitutional convention could unilaterally change the constitution without subsequent approval by the states. It couldn't. The convention is an end-run around Congress, not around the states.