To log into HathiTrust, visit HathiTrust.org and click the LOG IN button. You may need to select your institution, Ohio University, from a list. You will then be prompted to log into your OHIO account if you are not logged in already.
If you visit HathiTrust from its page in Libraries' ALICE Catalog, you will be automatically directed to your OHIO account, without having to choose your institution.
It is possible to search HathiTrust without logging in, but if you would like to build your own collection or download materials, you will need to log in.