Learn Hardcore Japanese: sanpokoosu no syuppatutiten wo kakuninsuru. - I check the starting point on the walking route.

Breakdown of sanpokoosu no shuppatsuchiten o kakuninsuru.

Is 散歩コースの出発地点を確認する a complete sentence, or is it more like a label/instruction?

It can function as a complete sentence in Japanese, but in many contexts it sounds like an instruction, checklist item, or heading.

確認する is the plain/dictionary form: to check / to confirm
Because of that, the whole phrase can feel like:
- Check the starting point of the walking route
- To confirm the starting point of the walking course
In manuals, schedules, apps, and bullet points, Japanese often uses the dictionary form this way.

In everyday conversation, you might more often see:

Why is there no subject, like I or you?

Japanese very often leaves out the subject when it is clear from context.

So this sentence does not explicitly say:

The listener or reader understands the missing subject from the situation.

For example:

This is extremely normal in Japanese.