What is the meaning of sizing a logic gate?
Sizing for example an inverter by a factor 2 means that you make both the NMOS and the PMOS in the inverter 2x as wide. This will behave in the same way as two standard (1x) inverters in parallel.

A 2x inverter will have a 2x stronger output meaning it can charge/discharge the load at its output (inputs of other gates) 2x faster.

So let's say that a 1x inverter can drive 10 inputs at a maximum speed of 100 MHz, 
then a 2x inverter can drive that same 10 inputs at 200 MHz or it can drive 20 inputs at 100 MHz.

That is roughly the idea.