Menu: Files->Open
Toolbar: 
Preprocessing:
With this command, a project previously saved with Save or with Save ASCII project can be opened.
Postprocessing:
Reads postprocess information in GiD. If, for instance, the postprocess files are 'PostFile.msh' and 'PostFile.res' and a view file is present with the name 'PostFile.vv' then it will be also read.
For big results files, GiD will use an index file to access the results information faster.
When Reading a file, under the 'Postprocess read options' this index can be rebuild:
The postprocess information can be in ASCII, binary, HDF5 (.post.res) or a file list (Filename.post.lst) specifying the post-process files to read. Sometimes, the mesh is separated from results in two ASCII files: .post.mesh + .post.res
The list file can be used to read several postprocess files at once. This includes both mesh, results and graphs files. The list file is just a text file, for a description of it's format please look at the Customization Manual under POSTPROCESS DATA FILES -> List file format.
When reading a file with lots of time-steps, there is an option to read only some of them:
By the default GiD reads all the steps of the analysis, with the value 1. If another number is entered, for instance 10, then one step every 10 steps will be read including the 1st step and the last step of the analysis.