You missed a lecture. Here is the order to catch up in.
You missed it. Maybe you were ill, maybe it was at 9am, maybe you just didn't go.
The usual advice is "get the notes from a friend," which is fine except it rarely solves anything. You end up with someone else's shorthand for a talk you didn't hear, and shorthand only works for the person who wrote it.
Here's a better order of operations, and an honest note about when to just let it go.
First, work out if it matters
Not every missed lecture needs catching up on, and pretending otherwise is how people lose a weekend to one hour of content.
Check three things:
Is it on the exam? Look at the syllabus or past papers. Some lectures are context, background, or a guest speaker. If it isn't assessed, skim it and move on with a clear conscience.
Is it load-bearing? Some topics everything later depends on. If this lecture is the foundation for the next four, it moves to the top of the list regardless of how it's weighted. If it's a self-contained aside, it can wait.
How far behind are you? One lecture is a Tuesday evening. Six lectures is a different problem, and you should triage rather than start at the oldest one. Go to the most recent, get current, then work backwards with whatever time is left. Being lost in today's lecture too is how one missed week turns into a missed term.
The order to try things
1. The recording, if there is one
Check first. Plenty of courses record and plenty of students never look.
Watch it at 1.5x. Don't take notes the whole way through, you'll just transcribe. Watch it, then close it and write down what it was about. If you can't, watch the bit you couldn't write about again.
2. The slides, used correctly
You'll have the deck even if you don't have the talk. Most people open it and read it, which does very little, because a deck is prompts for a speaker and not an explanation.
Use it as a table of contents instead. Turn each slide title into a question you'd have to answer, and you now have a checklist of what the lecture covered. That's genuinely useful even without the content, because it tells you what you don't know.
Then fill the gaps from a real source.
3. A friend's notes, with one rule
Get them, but don't read them passively.
The rule: go through them and mark every place where you can't follow the reasoning. Don't skip over gaps because the overall shape makes sense. That's the trap with someone else's notes. They're compressed for a person who was in the room, so the jumps feel smaller than they are.
Whatever you marked is your question list for the next step.
4. Office hours
The most underused thing in higher education.
You do not need a clever question. "I missed Tuesday, I've read the slides, I don't follow why we're holding capital fixed" is a completely normal thing to say, and lecturers generally prefer that to silence.
You also get the explanation in your lecturer's framing and notation, which is what the exam will use. No textbook or tool matches that.
5. The textbook chapter
Slower, but it has the explanation properly written out, which the deck doesn't. Find the section that maps to the lecture rather than reading the whole chapter.
6. Generate the explanation
This is what we build at Lecturly, so treat this paragraph with the appropriate suspicion. You upload the deck and it produces the narrated explanation that would have gone with it, roughly four minutes per topic.
It exists because the recording often doesn't, office hours are on Thursday, and the textbook is ninety pages. It's the fallback when the better options above aren't available. If the recording exists, watch the recording.
Don't do this
Don't copy out the notes. Copying is mechanical. You can do it with the TV on, and often the whole thing goes in through your eyes and out through your hand without stopping anywhere useful.
Don't read everything three times instead of testing yourself once. Rereading feels like progress and produces very little. Close the material and try to explain the topic out loud. Where you stall is what you actually need to work on, and you'll find it in five minutes instead of two hours.
Don't start with the oldest lecture if you're several behind. Get current first. Otherwise you're permanently studying material from three weeks ago while falling further behind on this week's.
Don't catch up perfectly on one lecture while ignoring four others. Partial coverage of everything beats total coverage of one thing, almost always.
The realistic version
For one missed lecture, an hour is usually enough. Recording at 1.5x if it exists, or the slides turned into questions plus the textbook section for the parts you can't answer. Then test yourself once, properly, with everything closed.
For a missed week, accept up front that you're not getting all of it. Pick the load-bearing topics, do those properly, skim the rest, and write down what you skipped so it doesn't surprise you in May.
Missing a lecture is normal. Everyone does it. The thing that actually causes damage is the two weeks afterwards where you avoid the topic because you feel behind on it, and it quietly becomes the thing you never learned.
Just start with the recording tonight.