how to open games when downloaded ?

This isn't really the forum for that. But what game format are you talking about, and what do you mean by open? View the filesystem?

Redump does not provide game data. We are a library of game metadata (such as hashes and titles), not actual data repositories.

However, "opening games" differs per console - for example, for Nintendo-based consoles, to view their files use a tool such as WIT for Wii/GCN, CDecrypt/DiscU for WiiU, etc..