You may consider functional annotation tools such as the one in DAVID where you can perform gene enrichment analysis and clustering. Other resources similar to DAVID are also available.
If you want to look for functions of specific genes, then, most databases provides gene descriptions, and you can add that to a list of genes with resources such as BioMart.
Assuming they have a known function, which most of them will likely not, you will need to compare them to existing databases.
I suggest starting with BLAST and its variants for closely related things, and then consider moving on to looks like hhpred or hmmer to find the more distantly similar sequences.
You may consider functional annotation tools such as the one in DAVID where you can perform gene enrichment analysis and clustering. Other resources similar to DAVID are also available.
If you want to look for functions of specific genes, then, most databases provides gene descriptions, and you can add that to a list of genes with resources such as BioMart.