Hi Ashraf
Yes you can use the H4N to record directly, it also has the option to plug in 2 external microphones.
However the correct mic to use, or if you use the H4N alone will depend on the location you are recording in, the ambient noise in the location, the amount of people you need to record simultaneously and the type of shots you require, in fact there are many variables you have to consider.
If you just need to record ambient sound, or a general audio then you should be OK with the H4N as the mics are omnidirectional. The quality is good and you can get great results. Bear in mind that 90 degrees is as narrow as the zoom records in terms of the mic pattern so you are picking up audio from a wide area. (You can switch to 120 degree if you need a wider pattern.)
You may be OK with just the H4N if you are recording a single voice as long as you can position it close enough although if there is high background noise this may not be ideal.
For more directional mics you then might want to consider a lavalier or lapel mic if you are in a controlled interview situation. However clipping a mic on to a subject is not always suitable.
Otherwise a well positioned shotgun mic like a Rode NTG2 or NTG3 or Sennheiser 416 these would usually be on a boom pole especially if your subjects move and held out of shot. However sometimes you can position them on a mic stand if the source of the audio is from one point and does not move much.
Additionally I would use something like a Rode Video Mic on your 5DMkII or loop a feed from the H4N if cables/situation allows to the camera.
This will give you pretty reasonable quality on the camera audio which allows for better syncing with software like PluralEyes etc. If you just rely on the camera internal mic and there is high ambient noise you may find syncing the H4N and the camera audio a struggle.
Sorry there is no simple answer to your question but hopefully that helps you consider a few options.
best wishes
Neil
http://www.patience.tv