Leave empty and the lead goes into the pool, where any colleague can take it.
New - waiting in the pool
Any colleague can take it from the board; from then on the board moves it through the pipeline.
The board is the usual way to move a lead through the pipeline. Accepting it happens with the Accept action on the board or in the info window.
Campaign attribution (UTM)
Tells you which ad or campaign brought this lead in. The intake widget fills these in by itself from the link the visitor clicked (?utm_source=…), so you only type them for a lead you enter by hand. The field names stay technical on purpose: they must match exactly what Google Ads, Meta or your newsletter puts in the link.