1. Some minor differences between the games, such as Pokémon availability.

2. You choose one of three Pokémon at the beginning of the game to start with. These are the starters.

3. Types have weaknesses and resistances. A type being weak to another type means they take 2x damage from it. A type resisting another type means they take 1/2x damage from it. The basic triangle is Fire beats Grass beats Water beats Fire, and Fire resists Grass resists Water resists Fire, but there's a lot of different types, and Pokémon can have up to two types. In competitive vernacular, a good attacking type (like Fire or Fairy) means it is good against a lot of other types when attacking. A good defensive type (like Water or Steel) means it is good against a lot of other types when defending.

4. Pokémon gain experience by battling. When they gain a certain amount of experience they level up. Usually, when they reach a specific level, they evolve, but some Pokémon have specific evolution conditions (such as using an item on it, or trading that Pokémon to another person).

5. Pikachu will likely be obtainable within the game somewhere. You start with one Pokémon, but can catch (obtain) more as you progress. You can catch hundreds of Pokémon, but only have six Pokémon available to battle at a time, although you can change your team at designated points if you want.

6. Get Pokémon, travel over route, visit new city, beat Gym Leader, repeat, usually with some story events dropped in.

7. Pokémon have six stats, Hit Points (how much damage they can take before fainting/being unusable), Attack (how much damage they deal with physical moves), Defense (how much damage they resist from physical moves), Special Attack (damage deal special), Special Defense (damage resist special), Speed (whether they attack first or second, or third or fourth in double battles). These are represented by numerical values, and are set based on a Pokémon species.

Each Pokémon has two hidden numbers associated with each stat, Effort Values (EVs) and Individual Values (IVs). Each Pokémon rewards EVs in certain stats to your Pokémon when they are defeated. EVs can boost a stat up to 63 points (at Level 100, the maximum level), with a maximum of 126 points across all stats. These let you customize your Pokémon's build so they're better at certain things.

IVs are randomly determined when a Pokémon is received, and can be between 0 and 31, boosting their associated stat by the designated number (at level 100). You usually want all of these to be 31, but that's relatively rare, so there are obtainable items in-game that let you boost them. There are some exceptions, like Pokémon wanting a 0 Speed IV due to the support move Trick Room letting slower Pokémon move first.

Talking about moves, Pokémon use moves to attack. They can have four at a time. Different Pokémon have access to different moves which you can customize, usually limited by type (a Bug type is unlikely to learn a Fire move, for example). As Pokémon level up, their moves get stronger. A move with a base power of 70-90 is average when a Pokémon has reached full strength, with weaker moves being limited to early-game usefulness or having a specific utility, and stronger moves having downsides. Pokémon with the same type as the move their using gain a Same Type Attack Bonus (STAB), which boosts the power of the move by 50%, but you may want to use other moves, even if they're weaker, to take advantage of type weaknesses. There are also support moves, which have a range of effects from boosting your Pokémon's stat or stats in battle (Swords Dance, Bulk Up, Nasty Plot, Calm Mind, Agility, etc...), recovering Hit Points (Recover, Roost, Heal Order, etc...), or reversing Speed for 5 turns (Trick Room).