The only thing you can do with spell points is create spell slots
Because all the standard spellcasting rules revolve around spell slots, the way spell points work is that you use them to create spell slots, and then you use those spell slots for whatever you would normally use them for:
You expend a number of spell points to create a spell slot of a given level, and then use that slot to cast a spell.
Other than this, there is nothing else you can do with spell points. They can't be used to directly power metamagic or anything else. The only thing they can do is create spell slots. The above passage only talks about casting spells by creating spell slots, but we can infer that any other feature powered by spell slots will work in the same way: first, you expend spell points to create a spell slot, and then you use that spell slot as described in the feature. (Note that converting spell points to a spell slot does not require any action. It happens as part of the same action that expends the created spell slot.)
Sorcerers can convert spell points to spell slots to sorcery points (at a loss)
So, as a level 3 sorcerer with spell points, you can create either 1st or 2nd level spell slots with those spell points. If you want to convert spell points to sorcery points, you must do so by creating a spell slot and then converting that spell slot to sorcery points as a bonus action. For example, you could expend 3 spell points to create a 2nd level spell slot and then convert that spell slot to 2 sorcery points. The end result is that you convert 3 spell points to 2 sorcery points, via a 2nd level spell slot that exists only as a transient intermediate state. Note that using a different spell slot level results in a different "efficiency" of conversion. For example, the 2nd level slot example here gives a 67% efficiency, while doing the same thing with a 1st level slot gives only a 50% efficiency, exchanging 2 spell points for 1 sorcery point. From what I can see, the slot levels that yield the most efficient conversions are:
- 8th level, at 72% efficiency (but this is likely a poor use of your single daily 8th-level slot)
- 5th level, at 71% efficiency (and no daily limit on the number of slots)
On the other hand, sorcery points can be converted into spell slots at the same rate as spell points. So sorcery points can sort of "substitute" for spell points one for one, but not the other way around. Regardless, you probably don't want to make spell slots from your sorcery points most of the time, because this will leave you with fewer sorcery points to use with metamagic and other unique sorcerer abilities. If you run out of sorcery points and want to continue using metamagic, you will be forced to convert spell points to sorcery points at a loss as described above.