If you have a file of just cash gifts then for the gift type mapping you would simply put a default value of "cash" in. In the case of the mixed file this is not possible.
The first method is simplest but less likely to be possible unless you want to manipulate the file (or are able to set up the file format). In the file you add a column called gift type which would contain the type of gift e.g. cash, pledge, recurring gift,etc. This would then map directly to the gift type field.
The other method would be to use data transformation. Say you are importing a mixture of recurring gifts and cash gifts and you have a frequency column you should map your gift type to the frequency column. You then go into the field settings and transform the frequency value into gift types. An example of this is shown below.
Note that this only works from version 1.9 patch 1. (released 6th June 2016)