Pokédex 3D, like most other Pokémon games, has you having to obtain the various Pokémon and collect them all as you go through. The methods you get different Pokémon are varied and require internet connection and various friends. When you boot the game up, you will receive 16 different Unova Dex Pokémon (Audino, Axew, Dewott, Emboar, Emolga, Foongus, Hydreigon, Minccino, Oshawott, Pignite, Samurott, Scraggy, Serperior, Servine, Snivy & Tepig), but to get all 153 Pokémon, you have to go through a variety of features.
AR Markers & Spot Pass
The most common and likely way of getting the rest of the Pokémon into your game is through the Spot Pass feature. Every day, you will get up to three Pokémon sent automatically through the Nintendo WiFi Connection. These three Pokémon are completely random Pokémon that you don't normally have, but there are ways to skew the Pokémon you get
For each Pokémon, there is an AR Marker. This marker is a simple marker which each Pokémon uses in order to appear in the Augmented Reality Viewer part of the game, but if you have yet to obtain the Pokémon, it will register it as a sticker in the sticker book. Now, this Pokémon has a higher chance of being chosen as the Pokémon obtained through the Spot Pass feature.
Transfer with Friends
The other method to obtain Pokémon is to transfer with friends. Here, you can use the options in the game to transfer the Pokémon locally with a friend who runs the Pokédex 3D game. This will transfer all the Pokémon you have to be catalogued in their Pokédex while theirs get catalogued within yours. This will allow you to fill up your Pokédex much faster than just waiting for the Pokémon to come up over Spot Pass.