What does this star symbol mean in Pokemon X Pokedex

StreetPass provides you with an amount of PokéMiles (PM) for each person you've met who is also playing a StreetPass enabled X or Y. PokéMiles can be traded in for items at the Lumiose City Pokémon Center. Alternatively, you can redeem them at the Pokémon Global Link website via the Game Sync feature of the PSS; the prices there are lower than in Lumiose, and the items you select will be delivered to the Pokémon Center of your choice. Eventually, you will be able to use your PokéMiles to play mini-games called "Attractions" on the Global Link website and win items, though at the time of this writing, no Attractions have been released yet.

To get rid of that green StreetPass light on your 3DS' homescreen, you have to go to the PSS (on the touch screen) and open up the Holo Caster (not to be confused with the Holo Caster item in your Bag). Once you're there, hit "check announcements." Then hit "Streetpass News" and you'll be notified of how many people you've StreetPassed, how many PokéMiles (PM) you got for that, and your total PokéMiles.

You can also earn PokéMiles by trading or battling with other players online (this includes Wonder Trade and GTS trades). The number of PokéMiles earned (either via StreetPass or online interactions) is based on the distance between the locations set on both players' systems; international interactions are worth more than local ones.

No, you are not using it passively :p.

To use the Pokemon Radar:

• You must be in tall grass. (This includes Flower grass, but unfortunately not the Route 6 grass, caves, or Water).
• You cannot be rollerblading.
• It must be fully charged. (After you use it, you will need to take about 50 steps before you can use it again)

Up to 4 patches of grass will shake. (It technically always chooses 4 spots around you but most patches of grass are smaller than it's range, so it may 'shake' a position that is not tall grass and therefore you will see less than 4.)

If you go into the shaking grass it is very likely that you will fight a pokemon. It is not guaranteed though.

After each battle four more spots will shake. If you choose a spot with the same pokemon as the last one you fought the cycle will continue. This is part of a chain.

Speculation: It looks like some spots will shake with more intensity than others. The less it shakes the less likely the pokemon in it will be the same as the one you just fought if there is any pokemon at all.

You will end the chain if:

• You start rollerblading.
• You run from battle.
• You encounter a pokemon that is not found in one of the shaking spots.
• You fight a different pokemon than the previous one.
• You do not find a pokemon in the shaking grass at all.

Helpful Tips:

• Repel and abilities like it will help prevent random encounters that may break your chain.
• Supposedly choosing the furthest away piece of grass is your best bet to find the same pokemon.
• You can catch any of the pokemon you encounter. It will not break your chain.

http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9_Radar