miRNA-Seq files header and expression values

[na_sd]

I have downloaded miRNA seq file from GSE31617
Files contain information like following:

hsa-let-7a-1 hsa-let-7a t0000020 25073 37013 5p TGAGGTAGTAGGTTGTATAGTT TGAGGTAGTAGGTTGTATAGTT S
hsa-let-7a-1 hsa-let-7a* t0059321 6 12 3p CTATACAATCTACTGTCTTTC CTATACAATCTACTGTCTTTC S
hsa-let-7a-2 hsa-let-7a t0000020 25073 37025 5p TGAGGTAGTAGGTTGTATAGTT TGAGGTAGTAGGTTGTATAGTT S
hsa-let-7a-2 hsa-let-7a-2* t1103419 1 1 3p CTGTACAGCCTCCTAGCTTTCC CTGTACAGCCTCCTAGCTTTCC S
hsa-let-7a-3 hsa-let-7a t0000020 25073 37128 5p TGAGGTAGTAGGTTGTATAGTT TGAGGTAGTAGGTTGTATAGTT S
hsa-let-7a-3 hsa-let-7a* t0059321 6 12 3p CTATACAATCTACTGTCTTTC CTATACAATCTACTGTCTTTC S
hsa-let-7b hsa-let-7b t0000335 3748 7938 5p TGAGGTAGTAGGTTGTGTGGTT TGAGGTAGTAGGTTGTGTGGTT S
hsa-let-7b hsa-let-7b* t0163422 2 2 3p CTATACAACCTACTGCCTTCC CTATACAACCTACTGCCTTCCC D
hsa-let-7c hsa-let-7c t0000721 2095 3068 5p TGAGGTAGTAGGTTGTATGGTT TGAGGTAGTAGGTTGTATGGTT S
hsa-let-7d hsa-let-7d* t0056459 6 18 3p CTATACGACCTGCTGCCTTTC CTATACGACCTGCTGCCTTTCT D
hsa-let-7d hsa-let-7d t0004262 320 767 5p AGAGGTAGTAGGTTGCATAGTT AGAGGTAGTAGGTTGCATAGTT S


First, I wanna know what is the header of columns? (files do not have any header line)
Second, I would like to calculate expression values for miRNAs, how can I do it?
Thanks

PS. I am new in miRNAseq files.

[GenoMax]

For ref Cross-posted: https://www.biostars.org/p/165320/

I am thinking that it is some sort of alignment format but the exact name is eluding me (and my google-fu for now). Hopefully some one else will be able to recollect.

Where exactly did you get that data file from on SRA?