Ofdm blocks in gnuradio

I am unable to understand how to connect flag input at the input
output side of insert preamble block in grc. How does that work

secondly there are ofdm blocks called sync pn, ofdm sampler, and ofdm
acquisition. seperately there is another block called ofdm demodulator
which does all the work of previous three mentioned blocks. so how do
use them? instead of using demodulator should we use three block
sepearately so as to see the operation better or is there something I am
doing wrong.

when I use sync pn, it has two outputs timing offset and freq offset .
where should i give those two outputs if i am connecting next to ofdm
demodulator block which has only a single input.

In a previous forum the entire ofdm blocks python file is given as

But now it’s not there in that directory. where should i find it.