How does meiosis and mitosis work and the DNA associated with it?

In genetics, the process of meiosis is a type of cell division that differs from mitosis. Does meiosis occur only in the creation of gametes? I don’t understand the concept of haploidity and haploid number and the number of chromosomes and the difference between an X shaped chromosome and a sort of L shaped chromatid. Are they both considered chromosomes? I understand that the difference between meiosis and mitosis is that homologous chromosomes pair up while apparently they do not in mitosis. Don’t they have to essentially pair up in the middle in mitosis in order to be pulled apart evenly into cells? Also, what constitutes homologous pairs, non-homologous pairs, homozygous and heteroxygous?