It's very straightforward. Just use the following link, obviously changing the latitude and longitude for yours. The z is the zoom index, you can play with it to get where you want.
I got this information by clicking on the "Link" button in the right hand corner above a map. This will also allow you to get the latitue and longitude for a location.
I don't know of a good way to make a marker on Google Maps, through the UI anyway. If you right click on a point and select "What's Here?" It will create a marker, but it will be to the closest thing (business, intersection, address, etc). This essentially performs a search with the latitude and longitude and returns whatever is closest to your search. A URL to do that would be:
With the q (for query I believe) being the coordinates where you want your marker.
A more effective method, if you are trying to send a link to a specific address would be to search for the address in Google Maps, which will give you a marker on the exact address and then use the "Link" button to get the URL for sharing.