No worries, learning is always confusing when you don’t know what you don’t know. The point about other apps it it can sometimes be confusing when people are very confident something unknown in Tinderbox exists. But, no harm done! To your questions:
Way back before Tinderbox moved from OS9-era frameworks to current Apple ones in v6, you could drag links between windows (this was also before the single app window vogue set in). When you dragged such link a line was drawn across the screen to show the link being made. simple and easy to learn. Also the app predates the more recent vogue for adopting wiki-derived link mark-up for plain text (i.e. the
The mono-window app and limitations of apple frameworks broke that older line-drag metaphor. Furthermore with only one window the link target was often off screen. So the old link-park mechanism was reworked to give us a link park on the tab bar. You drag to it to ‘park’ the stub of an incomplete link from the originating note.
This has some very useful properties. Say you want to link note A to notes B, C and D. Even if all 3 are visible it can be easier to drag from A to the link park and then once each from the link park to C, D and E completing each link as you go.
Tip. if you want to link from B to A and B is on screen, you can drag from B to the link and park and scrool to A and complete the link. When the Create Link pop-up shows use the double ended arrow next to the ‘To’ and ‘From’ labels to reverse the direction of the link.
The method using link park to many completions works best for basic (i.e. not-to-note) links. Text links (with an anchor text within $Text) generally go to one place. Text links give more targeted traversal whilst basic links are more use when mapping connections between notes (noting that the same notes can link via multiple links of different types and/or text links from different starting link anchors).
Again the recent vogue for wiki-style link mark-up brings in two further ‘learned’ limitations. A link doesn’t have to originate from text (as already described) nor does the anchor text need to be the title of the target note. The latter is a learned (false) assumption learned use more simple and less capable hypertextual systems where there truly is no choice.
Linking via actions
linkFrom("child"); is an action. Actions are used in agents, OnAdd, rules, edicts, and stamps. Explore the linked articles to see how these are used.
(side note for @satikusala the drag-drop linking nuances are something we should discuss)