Salesforce has two interfaces, the modern one that has been the standard since 2018 and the older one, called Classic, that has been in use for over a decade. Classic is being phased out by Salesforce, and no new features or functionality is being made available for it, and therefore all new work done on the ILR org is done with Lightning. There are a vanishingly small number of things, mostly related to financial operations that still require Classic, but for the vast majority of users, Lightning is a better choice.
You will know if you are using Classic if you see a link at the top right that says "Switch to Lightning Experience".
To switch to the Lightning interface: Click the "Switch to Lightning Experience" link
To switch back to Classic:
Click the face icon at upper right, and then choose "Switch to Salesforce Classic"
If you have difficulty accessing the information contained in this document or any document in this knowledgebase, please contact us at access-ilr@cornell.edu and we will assist you.