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Mitosis is cell replication into another identical cell. In humans, who have 46 chromosomes (23 pairs), it's the formation of another cell with the same number of chromosomes; another diploid cell. If you're looking for A level standard understanding, mitosis has 5 stages (interphase, prophase, metaphase, anaphase, telophase). In mitosis, at metaphase 1 chromosomes line up down the centre of the cell, then in anaphase the chromatids get pulled to opposite poles of the cell.
Meiosis is the production of gametes, or haploid cells, for sexual reproduction. In humans, this is the formation of cells with 23 chromosomes from cells with 46. Each cell produces 4 gametes. Then in sexual reproduction, two gametes (one from male one from female) fuse together in fertilisation. In meiosis, there are 9 stages (interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, prophase 2, metaphase 2, anaphase 2, telophase 2.) Metaphase 2 and anaphase 2 are identical to the stages in mitosis, and chromatids get pulled to opposite poles of the cell. However, in metaphase 1, instead of the chromosomes lining up individually down the centre of the cell, they line up in their pairs. In anaphase 1, the chromosomes get pulled to opposite poles of the cell (not the chromatids).
Hope that helps. All A level textbooks or websites will have this in.
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