How do I make a VCO with a LM 358?
Peter Bennett handled the first two questions admirably.


  I read that VCOs are tough to tune etc and are usually very complex to
  build. I don't know what means. Can I make this one easily?


This one is quite simple, although it's intended for fairly low frequencies and is not outstandingly linear over a large frequency range. VCOs can be challenging to build if a very wide range is required or extreme linearity (0.01%) or high frequency is required. You should be able to build this one on a breadboard.


  Does the 0.05 capacitor decide the timing of the output pulse? Can I
  change output frequency by changing the capacitor?


Yes, the capacitor value sets the overall frequency range. In this case, you'll get about 15 Hz/volt. If you double the capacitor, you'll halve the sensitivity.