sorting file based on two or more columns

Hi gang.

I'm using a unix/mac system and i'm trying to sort a file (more than 1,000,000 lines).

chr1    100000965       100001001       -
chr1    100002155       100002191       +
chr1    100002165       100002201       +
chr1    100002525       100002561       -
chr1    10000364        10000400        -
chr1    10000372        10000408        -
chr1    10000412        10000448        +
chr1    100004742       100004778       -
chr1    100004767       100004803       +

I want to sort the first column (text and it could be any of 24 chrom) and then sort by 4th column and then by 2nd column.

I tried sort command but when i type in sort +3 +1, it doesn't work.

sort -k3n,1 FILENAME

Thanks cfajohnson. it works. can you explain to me how the parameters work here?