most songs are made up of three or more chords, some songs even get away with only two chords! But how do you know which ones actually belong together? It does matter which chords are next to eachother, kind of like making a rainbow, if you put the colors in random order it won't look like a rainbow anymore; well music is the same idea, if you put any random two chords together it might not sound cohesive because they may actually belong in two separate key signatures.
Let's look at finding the titles of the other chords in a key signature. In all cases the first note of the scale you chose to use is going to be the title of your first chord, while the fourth and fifth notes in the scale will be the titles of the other chords that belong together.
The key of C major: C is the root chord, F is the fourth and G is the fifth.
The key of D major: D is the root, G is the fourth and and A is the fifth chord.
The chords can be played as a root on the piano but you will have to travel very far if you are using the first note as the first letter in the chord every time, so my favorite popular cadence pattern for the piano is super comfortable to play because it involves inversions https://www.siivers.com/post/how-to-play-inversions-on-piano of the 4th and 5th chord.
In the picture below the inversions have the same color for the notes that stayed the same.
If you play the root C in between each one you'll always have one finger that doesn't have to move! Not only is this physically easier to play more accurately but it also sounds super close together like it all belongs.