HI Nariman - yes, as Edwin mentions the best way to make things match up is to have Object Snap turned on (it will get that orange highlight on the button when it is on). When that is turned on, it should help you lock points on to existing geometry so that for example a line that you draw will be locked in to the right spot when you initially draw it.

If you're having difficulty with something in particular, can you please post an example model so I can get a better idea of what's happening?

- Michael