This card is treated as a Normal Monster while face-up on the field or in the Graveyard. While this card is face-up on the field, you can Normal Summon it to have it be treated as an Effect Monster with this effect:● The original ATK of this card becomes 2100.
Summon it once, end your turn, your opponent turn happens, once their turn is over and it's back to your turn don't summon anything and instead click on your Gemini and it will ask if you want to normal summon it, click it and it will have its effect.
Did u know what the gemimi mean in yugi or not !!! If not i will explain it. They are. Normal moaters in field and grave. But u can (RESUMMON then instead of do your normal summon) then he ill get his effect
So when u summon him he is a normal monster with no effect next turn u can re summon him and lose ur normal summon but the gemini get his effect
Lord 2022 is correct, but in simpler terms this card works like this.
Turn 1: normal summon him, at this point he is treated like a non-effect monster.
Turn 2: you can activate his effect and "resummon" him as an effect monster to gain the 2100 Atk.
*Keep in mind that "resummoning" takes place of your regular summon that turn.