IMRaD is a convention that lets a reader find what they need without reading everything. Each section answers one question.
Introduction — why did you do this? Funnel from the broad area to the specific gap to your question. Ends with your question and hypothesis. No results here.
Methods — what did you do? Past tense, enough detail to replicate. Materials, procedure, controls, sample sizes, statistical tests chosen. No justification of why the method is good — that is Discussion.
Results — what happened? The findings, with statistics and figures. No interpretation. "Group A grew 34% taller than group B (p = 0.003)" belongs here; "which suggests nitrogen was limiting" does not.
Discussion — what does it mean? Interpretation, comparison with prior work, limitations, and next steps. Every claim here traces to a number in Results.
The most common misplacements: interpretation in Results, results in the Introduction, and new data in the Discussion. When a sentence feels awkward, check whether it is answering the section's question — usually it belongs one section over.