Simple question: how to snap to lines, guides, intersections?

I ma drawing some clipping masks, shapes in illustrator. There is some design already drawn. I want that new shape corners alight to other objects, guidelines, etc. If I draw them vaguely by an eye only, then when zooming im I see that object starts 21.00009 mm when it has to be 21mm and often a hair thin line from another object layed behind will be still seen when in print.

It would be helpful if my shapes would snap to other objects, guides, whatever same way as it is in InDesign.

how can I sconfigue Illustrator in this way, and how to control this behaviour???

I have used Visio befoe and had no problems whatsoever. On new job, we have Adobe packages, but I do not see Snap to Grid, Snap to Guides in the menu. 

Thanbk you