In the above Punnett square, the genotypes are found by concatenating the parent alleles.
For example, in the top left square, EA crosses with EA, so the genotype is EA+EA=EAEA. To facilitate comprehension, we group together similar alleles (here E before A), so it became EEAA.
Another example, is the bottom left, EA crosses with ea gives EAea, and when arranged (E before A), we get EeAa (capital, or dominant allele always first).
1. eA+EA => eAEA => EeAA
2. EA+Ea => EAEa => EEAa
3. Ea+Ea => EaEa => EEaa
4. eA+eA => eAeA => eeAA
5. ea+ea => eaea => eeaa