I'm not too sure what you're asking here but I'll try to answer this using my understanding of the question.
First, it's important to define genotype, allele, and phenotype.
Genotype: the genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits.
Allele: any of several forms of a gene, usually arising through mutation, that are responsible for hereditary variation.
Phenotype: the appearance of an organism resulting from the interaction of the genotype and the environment.
Alright so let's unpack that and translate it to english. So genotype refers to the genes an animal carries and can refer to a single gene or a group of genes. An allele is the form of the gene you have (ex. a "hair color gene" has several alleles such as blonde and brunette. Either way the gene is a "hair color gene" but there are different forms of that gene corresponding to different hair colors.). For all genes except those carried on sex chromosomes, everyone has two alleles which may be the same or different.
Phenotype is a bit more complicated. Alleles can be passed down from parent to offspring which can affect the appearance of the offspring. However, recall that everyone has two alleles for each gene (except for those carried on sex chromosomes). Each allele of a specific gene in an individual has a 50% chance of being passed down. Following the previous example, if one person has one brown hair allele and one blonde hair allele, they have an equal chance of being passed down (50/50).
Now, once you have these genes and you're born and out in the world, phenotype can still change! This is referred to as epigenetics. If you are in grade school (excluding AP bio), I doubt that you have heard this term. I don't want to confuse you so let me know if you want an explanation for epigenetics as well.
Alright let's put this all together!
So each parent has a particular genotype, or combination of alleles. One of two of these alleles are passed down from a parent to either a sperm or an egg through a process of cell division called meiosis. So we've got one allele from mom and one allele from dad. The sperm and egg then combine which results in a child with two alleles (one from mom and one from dad). These two alleles then become an observable phenotype.
Alright example time:
Dad has two alleles for blue eyes.
Mom has one allele for brown eyes and one allele for blue eyes.
When the mom is creating eggs via meiosis, there is a 50% chance any single egg has the allele for brown eyes. Therefore, there is also a 50% chance the egg has the allele for blue eyes.
Since dad has two alleles for blue eyes, there is an 100% chance that his sperm has the allele for blue eyes.
*Note: So here we are translating phenotype (eye color) to genotype (allele).*
So one sperm from the father combines with one egg from the mother which carried the allele for blue eyes.
The child then has two alleles for blue eyes and consequently has the phenotype of blue eyes.