Youtube offers several ways to line up videos so that they will play one after another. Save to Watch Later and Save to Playlist are the most well known ones and are present across in Youtube on all devices. A lesser known web-only feature is the Add to Queue which works only on the Youtube desktop website. Youtube's mobile apps for Android and iOS do not support the Queue feature. You can either use the "Save to Watch Later" or "Save to Playlist" feature, as an alternative to the missing Queue feature.