Why it has used BPSK modulation after OFDM?

I am quite new to OFDM modulation. I am reading this from a tutorial. In one of its parts, for showing amplitude variation of the OFDM signals, there is a graph that has used 8 sub-carriers and BPSK modulation as below:

Now I have faced to this question, that we are using OFDM modulation here, so why we have used BPSK modulation? Do we double modulate the signal? I cannot understand the use of BPSK in this example. Any help?