Q: How can I log in to my iPad through different Apple ID?

What do you mean by 'log in to my iPad' ? You can tap on account id in Settings > iTunes & App Store and log out of it and you can then log in with a different account so that you can use a different account in the stores.

All content that you download from the store is tied to the account that downloaded it, so if you do log in with a different account then your existing apps will remain linked to old account, and only that old account can download updates to its apps. Using iTunes Match, automatic downloads and/or redownloading an account's past purchases may tie your iPad to that account for 90 days (so you won't be able to do any of those three things on a different account until the 90 days have completed) : http://support.apple.com/kb/HT4627