Basically, a reading frame is the result of DNA or RNA nucleotide sequencing in non-overlapping triplets. It's like taking the strand of DNA and / or RNA and stretching it into a straight line. Thus, all nitrogenous bases would be in sequence and aligned as in a row. Each three nitrogenous bases (codon) encodes a protein.
The reading structure has revolutionized the field of genetics and evolution, since we can see the sequencing of the genes of individuals, we can make comparisons between their DNAs to discover possible evolutionary relationships between them. In addition, it is also very important in medicine to locate sequences where there are genetic mutations (base exchanges or subtractions).