The Player's Handbook (p. 101) states (about flexible casting):
Creating spell slots. You can transform unexpended sorcery points into one spell slot as a bonus action on your turn.
I'm unsure how to interpret this in practice. Does this mean that you can gain more spell slots than you would normally have available after a long rest, or would you only be able to regain expended spell slots up to your normal maximum? And if the former, would the excess spell slots be lost on a long rest or not?
How to interpret the Sorcerer's Flexible Casting ability that utilizes Sorcerer Points to create Spell Slots:
"...As a bonus action on your turn..."
Which doesn't go to say that every spell ever that takes a bonus action or action on your turn can't be used out of combat, but we can assume they stress this point due to its combat applications. Creating or burning spell slots doesn't have too much out of combat usefulness. You would interpret this as a combat ability, and an out of combat utility that can be useful in certain situations.
Each Spell Slot that you are able to craft through the use of Sorcery Points takes an amount of SP only acquired once you are of sufficient level to even have that level of spell slots available to you. So while you could never have a spell slot that's beyond your ability to use at the time, its primary use is replenishing spell slots that you've cast or otherwise used up in battle (as when you burn one to gain more SP so you can put them into a Meta Magic ability). They do not roll over , as it were, as taking a long rest basically returns everything to its normal state. Extra spell slots disappear, Temporary HP disappears, and any temporary buffs or bonuses that were applied through magical means disappears; unless it has an effective duration exceeding your Long Rest period. Flexible Casting spell slots are no different.
So yes, the rules don't say anything about not being able to exceed your normal maximum allotted spell slots. Taken as written, if you wanted to burn all your SP at the beginning of a combat to gain all those extra spell slots, you could do so, but yes; they are lost on a long rest. No slot hording for you!
I hope this helped in your interpretation of the ability and the rules. I have a Sorcerer in my adventuring party and I'm kind of jealous of his raw magical power. He's a beast with those Twin Spell and Quick Spell Meta-Magic feats, and we won't even touch on Magical Missile...
You can use those points to gain spell slots the cost listed, and you can expend spell slots to gain sorcery points.
You can load up more spell slots than you start with so you could at 1st level instantly expend your 2 sorcery points to add a 3rd first level spell slot.
If you never cast anything before a long rest you would regain all sorcery points and all spell slots, and excess spell slots would be lost.
If they could keep the spell slots sorcerers would be able to spend their downtime loading all their sorcery points into spell slots and go adventuring with hundreds of spells available.
Basically it will let you create a spell slot on the fly, by expending unused sorcery points, or you can burn an existing spell slot to gain sorcery points.
For example:
You need to cast a 5th level spell, but you have no more slots of that level available. You can burn a 7th level slot to gain those points in your sorcery, and then use them to create the 5th level slot. You could also burn a 3rd and 4th level slot to get the 7 points necessary instead.
Alternatively, if you need a lower level spell slot and have sorcery points to burn, you can spend some sorcery points to gain another lower level spell slot. You may also use sorcery points to get "extra" slots (At least the rules don't say otherwise), so if you have 4 level 3 slots and you need another, you can use sorcery points to gain it.
All this is on a daily basis, so once you are out of points/slots, you are done until you rest, at which point everything resets back to your baseline.
