The HTML tags TITLE and ALT are used on text and image links respectively to give a description to the link or image. ALT tags are also used describe an image. The title tag is suggesting a title for the destination source. Both tags are displayed by different browsers in different ways and also auditory browsers can read the text aloud.
It has long been known that some of the search engines associate ranking and relevance to the target page based on TITLE tags on the links that link to that page. This is therefore tied in with the text that is used to link to pages. The TITLE is meant to be a more descriptive passage on that link target and the text used to link to that page. So here again we should try to incorporate keywords and key phrases for that target page in the TITLE tag.
To add text into the USC TITLE tags for a given link, the text needs to be added into the Tooltip field of the link
ALT tags have a similar effect to TITLE tags but just on the images they relate to. The text entered in an images ALT tag can be used by search engines for image indexing but also an indication of what the image content on that page relates to.