What is the differnce between genotype and phenotype, and how are they linked?

The genotype is all of the genes in an organism. If, for example, you're interested in eye colour, the genotype for eye colour is the sequence of DNA that says 'eyes will be blue' or 'eyes will be brown'. The phenotype is all the observable traits that results from the genotype's instructions, eg eye colour.
For genes actually tell the organism what to do, the instructions that are kept so carefully in the chromosomes in the nucleus have to be taen out into the cytoplasm, where things actually happen. So the gene is transcribed into messenger RNA (mRNA), which is similar to DNA but single stranded. The mRNA leaves the nucleus and into the cytoplasm (or the ER), where it meets ribosomes. these are protein complexes that read the RNA sequence and translates it into an amino acid sequence, making a protein. Going back to they eye colour example, the DNA (genotype) could encode a protein that make eyes brown, and as it is transcribed and then translated, the protein is synthesised, and the phenotype appears: brown eyes