Each character is born into a race, ranging from the often aloof Elves to the stout Dwarves. Your character’s race establishes their general appearance and their natural talents, gained from their culture and ancestry. These include ability score increases, special senses, proficiency in certain tools or skills and even in some cases access to minor spells. It also tells you what languages you know and what your base speed is.
More detailed information can be found in Chapter 2 of the Player's Handbook.
In Tasha's Cauldron Of Everything, a recent Sourcebook released by Wizards of the Coasts, has released an option that allows you to customise these options to make them more flexible with other classes.
This includes being able to adjust the allocation of the ability score increase granted by your race. Instead you can apply the stated ability score increases to more preferable stats.
Please Note: Scores cannot go over Level 20 and you cannot apply multiple score increases to the same ability.
The following example works on the idea of you playing a Dragonborn Ranger.
The Dragonborn naturally gives you two ability scores increases of +2 to Strength and a +1 to Charisma. However the Dexterity and Wisdom abilities are more important to a Ranger. Using Tasha's new ability you would be able to change your Ability Score increases to a +2 Dexterity and a +1 to Wisdom.