The "IGF1" at the front indicates that the genetic variation is in the gene for Insulin-like Growth Factor 1. The notation (CA)n is used to describe n adjacent repetitions of the two-base sequence CA (Cytosine, Adenine) present in a particular IGF1 DNA sequence. Hence IGF1 (CA)19 / (CA)19 is referring to a genome in which both copies of the IGF1 gene have 19 adjacent repetitions of the CA pair of bases, that is, which is homozygous for IGF1 (CA)19.
Such a repeat is usually called a microsatellite or Short Tandem Repeat (STR). They are common sources of variations in genes because the DNA matching process during meiosis sometimes "slips" one or two repeats over.
The type of test performed by 23andMe reports values for selected SNPs (Single Nucleotide Polymorphisms). SNPs are a different kind of variation from STRs, so the data available from 23andMe does not allow you to determine the kind of IGF1 (CA)n variant present.