For example: GGATACCTAGGTAAT
Insertion: GGATGACCTAGGTAAT
a nucleotide that was not present before is inserted into the original sequence
Substitution: CGATACCTAGGTAAT
the first nucleotide was substituted in for another (C for G)
Frameshift (basically a insertion or deletion, we'll try deletion here): GATACCTAGGTAAT
the first nucleotide was deleted, causing the reading frame to be shifted (instead of GGA as the first codon, we have GAT)