When do tantrums start?

Not sure if my little one is starting to try to test the waters. I noticed the last couple days he's been crying and screaming when he wants to be picked up or even getting out of the car seat. At first I thought it was just because we were driving back from California to Texas so I figured the tantrums were just cuz he was over being in the car. But even today after waking up from his nap I held him for a bit and then I put him in his bouncer so I can pack the diaper since we have errands to run today And he was just not having it. Not sure if this is just a phase or what I don't want him to think that crying and screaming is going to get him what he wants He's never acted like this before so it's all very new to me. Also I would like some advice on how to handle it so he doesn't think that screaming and crying is going to get him his way. He will be 9 months in 2 days so any advice helps 😅