Start the Google Map app.

Next put in your destination in the white box at the top of the screen.  Google might find multiple locations that match your destination, tap the one you want.

If you want to change the starting point from your current location to some other one, then tap the  “Your Location” block near the top of the blue area and enter the desired starting point.

If you want to change the departure time from the default of the next bus, then tap the clock at the bottom of the blue window on the left.

Now tap on the desired schedule and a map will pop up showing the routes.  At the bottom of the screen it will tell you what buses and the walking times to the first bus stop for all the routes that seem to meet your requirements.

Now tap on the “bull's-eye” on the lower right of the map.   That will center the map on where you are.  Now follow the blue dots to the bus stop.  North is usually at the top of the map. 
Sometimes you will be in a place that you do not know and you will have trouble orienting the map.  In that case just walk a block and see how you moved on the map.  Knowing that, you should have to trouble getting to the bus stop.  For some reason Google does not give turn by turn directions to the bus stop when you select travel by bus as your mode of transpiration. If you had selected walking and put in the bus stop it would give you turn by tern directions but that is a very awkward way to work the problem.