A cell's DNA holds the instructions for every protein it can build, but the machinery that actually builds proteins — the ribosome — sits outside the nucleus, and DNA itself never leaves it. Getting an instruction from the archive to the factory floor takes an intermediate step: transcribing the gene into a disposable working copy, then reading that copy to assemble the protein.
Transcription: copying one gene, not the whole book
Transcription is the process of copying a single gene's DNA sequence into a molecule called messenger RNA, or mRNA, carried out by an enzyme called RNA polymerase that reads the DNA template strand and builds a complementary RNA strand one base at a time. Only the section of DNA covering the gene actually being expressed gets transcribed — not the whole chromosome — which is part of how a cell controls which proteins it makes at any given moment, since a skin cell and a neuron carry identical DNA but transcribe almost entirely different sets of genes. In cells with a nucleus, the finished mRNA is processed and edited before it's allowed to exit into the cytoplasm, where the ribosomes are waiting.
Translation: reading the copy three letters at a time, then discarding it
Translation is where a ribosome reads the mRNA sequence three bases at a time — each triplet called a codon — and matches each codon to a specific amino acid, using transfer RNA molecules as the adaptors that physically carry the right amino acid to the right codon. The ribosome strings the amino acids together in the order the codons specify, producing a chain that folds into a functional protein. Once an mRNA molecule has been translated, often multiple times by multiple ribosomes in succession, cellular enzymes break it back down — it's a working copy, not a permanent record, and making a new one each time a protein needs to be produced again is part of how the cell keeps control over how much of a given protein actually gets made.
What we're still unsure about
The core mechanics of transcription and translation are among the most thoroughly confirmed processes in biology, replicated across an enormous range of organisms, but the regulation layered on top — exactly which genes get transcribed, how strongly, and in what sequence, in response to a given signal inside a given cell type — is still an active, only partially mapped research area. A meaningful share of the human genome doesn't code for protein at all, and what much of that non-coding RNA is actually doing to regulate this process is a live and genuinely unsettled question in molecular biology, not a footnote with a known answer.
This sits inside Transcription & Translation, one of eight topics in Genetics, one of six domains in Biology, one of seventeen subjects the app can quiz you on.