I can never remember the order of the columns in samtools, so here they are
- QNAME: Query name of the read or the read pair
- FLAG: Bitwise flag (pairing, strand, mate strand, etc.)
- RNAME: Reference sequence name
- POS: 1-Based leftmost position of clipped alignment
- MAPQ: Mapping quality (Phred-scaled)
- CIGAR: Extended CIGAR string (operations: MIDNSHP)
- MRNM: Mate reference name (‘=’ if same as RNAME)
- MPOS: 1-based leftmost mate position
- INSIZE: Inferred insert size
- SEQ: Sequence on the same strand as the reference
- QUAL: Query quality (ASCII-33=Phred base quality)
There are lots more details in the samtools manual
You should also use the samtools flag explainer to understand column 2