Your initial confusion is a common one. NaNH2 with NH3 as solvent is a strong base, good for deprotonating things like alkynes. Na° with NH3 is something completely different - it is a reductant, good for reducing alkynes to trans alkenes.
NaNH2 is an anionic nitrogen atom with two hydrogens, two lone pairs, and a negative charge. This is what is used in this question, and on the Master Organic Chemistry site.
Na° is elemental sodium metal with its one 3s valence shell electron. This is not what is being used here, but is what is being described on the assignmenthelp website.
They sure look like the same reagent, but they are not, and when they're written in line with the rest of the reagents, it can be hard to quickly see the difference. And sometimes the "°" isn't written next to the Na! Make sure to re-read these types of reagent to make sure you're using the correct reagent.