The symbol ":-P" represents a (mostly) friendly smiley with a stuck-out tongue. It is often used in chat for flirting.
The 😛 smiley is one of the cheekier variants of its kind. The observer only has to tilt his face slightly to the side to see that a tongue is hidden behind it.
Accordingly, the 😛 is mostly used when it's a matter of teasing the other person a little or, if necessary, drawing them out.
The 😛 smiley is one of the older symbols of its kind. The face with the stuck-out tongue followed comparatively quickly on the grin variant and helped to be able to express the sender's feelings a little more specifically.
Since the spectrum of "cheeky smileys" has expanded significantly over time, the 😛 smiley is no longer the only way to be a little flirty on the go. So it's worth looking around a bit and, if necessary, also trying out the kiss smiley and other faces.
But be careful! The use of smilies - especially in flirt chat - should be handled with care. A grinning face here and there can lighten the mood and be fun, but: If you ONLY send smilies, you will quickly appear unimaginative to your virtual counterpart. Therefore, witty texts should alternate with the popular faces. Otherwise, communication will quickly get bogged down.
Another point: interpretation. Most smilies offer a lot of leeway when it comes to drawing conclusions about the respective statement behind the "bracket, hyphen, letter" combination. If in doubt, ask here. Nothing is more annoying than having to get angry about a wrong interpretation of a smiley.