a mutation occures in the gene Dna polymerase. if the mutation is deleterious what would be the effect of the mutation on the cellular process that the protein contributes to ? what if the mutation was substitutions

Sounds like homework. Lookup what a DNA polymerase is doing (hint: PCR). I assume here that the DNA dependent DNA polymerase is meant (instead of the viral RNA dependent one). The second half sounds incomplete.

its not homework but thanks for the help

DNA polymerase probably aids in the process of DNA replication, so if gene for this protein (DNA polymerase) suffers from a deleterious mutation, probably few amino acids which should have appeared in the sequence would be missed, and if such amino acids are vital to the function (activity) of the enzyme, the cell would probably get error during DNA replication and thus also affect the cell division process.

while, if the mutation is substitution, the effect would be less negative, in some case, I think. as if the substitution does not affect the sequence of amino acid in the result protein (one amino acid is usually coded by more than one codon), I think there is no much harmful effect; however, if such substitution change the amino acid sequence and unfortunately alter or destroy the function of the enzyme, the effect would be as same as mentioned above when a deleterious muatation occur to the gene.