Is it okay to handheld a macro lens and snap pictures while walking?
Most people said a macro lens need to be on tripod to get good macro
pictures.


If there is enough light go for it! I take my 100mm f/2.8 out whenever I want that 2.8 aperture and sharp results (especially stopped down a bit). Basically you should have no problem till f/8 or so (subject will vary greatly), then you might have to start pushing the ISO so that noise becomes a consideration. Most people can handhold 1/250th, 1/90th on a good day, so pick a safe shutter speed and work out the rest of the exposure triangle however you like, or can, for the conditions. Obviously a tripod buys you shutter time enabling a lower ISO or a small f stop (f/16 - 32).


I suggest you read the book Understanding Exposure, and start thinking about a flash (off camera).


-sHEA