40d:Stairs

Stairs allow dwarves and other creatures to travel up and down. Ramps most likely operate in the same fashion and so most advice here should apply to both.

Constructing Stairs

In order for stairs to be usable, you must construct stairs on both levels you wish to connect (An up stair connecting to a down stair). However, a Down or Up stair will give you sufficient access to the adjacent level to build connecting stairs. This means you can dig directly downwards or even directly upwards using stairs without needing any other forms of access to the area.

Using an Up/Down stair (Which goes both up and down on the same tile) you can dig a straight vertical shaft.

Only upstairs can currently be removed through the designation menu but a new floor can be built over a downstairs to effectively remove them.

There are two ways to construct up stairs - through the Designation menu and through the Build-Wall/Floor/Stairs menu. You use the option in the Designation menu when you want to create up stairs in an area that has not been mined out. You use the option in the Build menu when it has. Down stairs can be constructed in mined out areas with the Designation menu, however.