So RNA doesn't create amino acids - they already need to exist (and there's a lot of metabolism that explains where they come from). What the RNA does is tell a piece of cellular machinery to combine the amino acids in a specific order to make a protein.

Depending on the organism, there are a few ways to do this. If you have a simple organism, like an archaeal cell, here's how it goes:

The DNA is all one giant circle. That circle has maybe 3 million bases, or 3 megabits. Those three megabits maybe encode 4000 or so distinct protein-coding genes. There's also some space between genes. Even though it's a circle, it is directional because the molecules connect in a specific way (5' OH-3'OH but that's just details).

That DNA is sequences of four bases, which we represent by the first letter of their human names - A for adenine, T for thymine, G for guanine, and C for cytosine.

If we wanted to denote a stretch of DNA that goes Adenine-adenine-guanine-adenine, we'd write AAGA. The cell obviously has no idea that's what it is, but it can read the topology that stretch of DNA would make. i.e., the cell recognizes the shape of that specific sequence of DNA.

OK, so we have one giant "file" with 3 million A, T, G, and Cs in there. Inside that file, there's roughly 4 thousand functions (proteins) that we can check. And just like humans, cells have developed syntax.

To get just the RNA we need, i.e. to call a function, the cells look for the following DNA sequences (they all vary a little depending on what organism):

The BRE: CCCTCC. A specific protein called "Transcription Factor B" recognizes this and grabs onto it.

The TATA box: TTAAAATTA. A specific protein called TATA-binding protein will bind this.

The BRE and TATA box are a little bit in front of each gene. So they appear some ~4k in the genome, before each protein-coding gene. (this is simplified but you get the idea). The job of those spots is to be bound by their partner proteins, and those partner proteins then will instruct the cell to copy the corresponding gene (usually right next to them) into RNA. Once you get to the end of the gene, there's a terminator sequence[0] which the proteins that are copying the DNA into RNA get blocked by, and can go no further. So that's how you get just the RNA for your gene.

Now - the RNA can go to the ribosome to be "translated" into the protein. This is where the triplets come in. The first triplet is usually AUG, which codes for the amino acid Methionine. That's called the "start" codon. However, imagine our RNA sequence looks like this:

AUG CAA ACC AUA CAA GUA UCC AAA ACG GAG CUG AAG UCC CUC GCU

That should code for the following protein, where each letter indicates an amino acid:

MQTIQVSKTELKSLA

But we have a problem. How on earth do we make sure that the ribosome starts at AUG? What if it instead started at UG C, essentially "slipping" by one base? Then, our protein would be totally different, and would look like this:

CKPYKYPKRS.SPS

So organisms also transcribe, at the beginning of the gene, a "ribosome binding site", or "Shine Dalgarna/Kozak" sequence. That sequence looks like this:

AGGAGG

So your whole gene now looks like this in RNA form:

AGG AGG AUG CAA ACC AUA CAA GUA UCC AAA ACG GAG CUG AAG UCC CUC GCU

The AGG AGG makes sure that you bind the RNA in the right spot, and start reading from the "start" codon (AUG) until you reach the end of the transcript.

[0] The terminator sequence is tough to conceptualize, and not every gene uses it, but essentially its a bunch of self-complementary bases that when the DNA is unwound for transcription to RNA, they knot back up on themselves so the proteins that are converting DNA to RNA can't go any further. See the image on this page:

https://parts.igem.org/Terminators