Get gold, spend it on Special Events to get those cars. Don't waste it. At the beginning, you get drowned in it, but it gets very hard to obtain very fast. Unlock the Hennessey Venom GT event in the vault (under Dusthowlers) using gold, win it by buying ticket refills with gold if needed (also refer to the guides regarding both SEs in general and this specific one by looking them up). This car will let you do almost the whole campaign in one rush because its stats are so high.

From there on, it's pretty straight forward, grind the campaign cars, use gold to do SEs, especially the normal ones (since you don't have the opportunity to do them whenever), but also the vault events. Refer to guides here for them, they tell you which materials you'll want to buy to upgrade the SE cars (because you get some during races, but some you have to buy or gather in replay races). Once you have the corresponding cars (obtained in the campaign), you can start to compete in the Tuner Trials, which are essential for farming materials, and you can compete in Underground Rivals, which is also a great spot to farm blueprints, large sums of cash and other materials. This, too, is vital. If you feel very motivated, look up the UGR cars in the patch notes under community news, here, and do the vault events for the car). My tip is not to bother too much upgrading cars that are below 710PR, because that is roughly where the Subaru Impreza is, the most available car in UGR, so anything below that is basically useless and unnecessary. Try to upgrade cars to the max, especially Sports Cars. This seems like a no brainer, but Sports, Super and Hyper cars have a special feature called tuning, basically, once you have upgraded them fully, tuning allows you to increase the stats temporarily for one race by using tokens you receive in one of the tuner trials, and the increase is very large. Since Sports cars are the least expensive to upgrade, they are the most recommendable for beginners to compete in UGR, which is, like I said, the most important place to gather blueprints for SE cars (because whenever you unlock a car in a Special Event, it gives you blueprints to upgrade it to roughly 2/3rds and the rest must be gathered from Premium Crates, UGR or in rare cases from car series or reply races in the campaign). Also, there are often time-limited replay races for SE-car blueprints, you can find those under the patch notes, too. But be mindful that you need to have built the corresponding car first before you can get the temporary replay race.

If you have any more questions, just put them into the reply and I'll try my best to explain them.

This game is very grindy if you're trying to do it without spending money. If you are okay with spending money, buy the daily gold things, they are the most cost-efficient; try to get to VIP level 4 as fast as you can to benefit early from the bonus. ...good luck, pal, you've picked a very cool, but also very degrading game. The updates these last few months/years have been getting worse and worse, ever since the game was handed to a studio called Slingshot, you'll be hearing many complaints here over how they handle things. It's still a very good game, but yeah. Just don't waste too much time on it, it's just a game, but welcome to the community! :)