how to open .hdr file

l'm a new learner ,l want to know how to open hdr file and what's the files of hdr and nill.

Thank you very much if the teacher can tell me!!! 

Nii and img/hdr pair (note the img/hdr pair is one format that can not be fragmented) represent two different NIFTI formats, for more information please see.

In general, these two formats of image files can be opened and read in most of the current software, for example, SPM8/12, REST, DPABI, MRIcroN, FSL, and AFNI, etc.

For their mutual conversions, many software/codes can do a very well job, for example, MRIConvert, fslchfiletype command in FSL, dcm2nii.gui in MRIcron, 3dcalc in AFNI, etc. 

Take the REST toolkit as an example, you could try clicking the “hdr info” area in the upper-left corner of the slice-viewer panel. Other ways to read the information include employing the MRIcro and MRIconvert toolkits. I do not know if this way always works, the best maybe that extract those from original DICOM data.