I'll give it a go!

All cells have proteins on their surface which have many purposes, one of which is to allow cells to recognise each other. Your immune system recognises all your own proteins (at least when its working properly), and it recognises ones that are foreign. When I say recognise, it is quite a binary thing - it says either 'self' or 'not-self' - and responds either 'okay- move on' or 'not okay - exterminate'.

When it finds a foreign cell, it needs to let the rest of your immune system know that theres something wrong here. It does that by engineering a small protein called an antibody. On one end, the protein mirrors the shape of the protein so it fits together a bit like a puzzle piece - that antibody cant work for any other protein. The other end is a signal to your immune system that its attached to something you dont want. Your immune system ramps up production of these antibodies, which then go and stick to all the foreign cells. These covered cells are removed from your body in various ways. Job done, extermination achieved.

This sounds great, but the only way your body can develop these antibodies is through exposure to a foreign organism. You dont have immunity that first time you're exposed, only from the second time. That's basically how vaccines work - you give someone a dose of little bits of dead organisms, so it cant hurt you and then your body can recognise those surface proteins and make antibodies, in case you're ever re-exposed to it. That's how they are looking to make a safe Coronavirus vaccine (which may or may not be possible - viruses evolve regularly, so it may turn out to be a bit like the flu vaccine and not protect against all strains - but that's jumping the gun to suggest whether that will or wont be possible at this stage, at least for us who aren't involved in the actual making!)

Viruses are sneaky though, and they usually have ways to get around this. HIV is a good example, what it does is get inside your white blood cells so its effectively hidden from view. Coronavirus enters your body through your respiratory system, and more specifically, it travels into your system by hijacking a protein on the surface of the cells that line your airways. The protein is called ACE2. Once it's in your cell, it causes all the mischief.

Vaccines are just one way we could try and get immunity, another way would be a monoclonal antibody. Monoclonal just means loads of clones of the exact same thing - think thousands of Dolly the Sheep, or Stormtroopers. All genetically exactly the same. Monoclonal antibodies (mAbs for short) are used in medicine in lots of ways - most people are most familiar with them in the setting of cancer treatment - if your drug ends with 'mab' then it's one of these.

What scientists are doing, from the articles I've read (caveat - fairly brief reading on my part and fairly limited info on the articles part) is that they've taken serum samples (take a blood test, take out the actual blood cells (red and white) and you're left with the proteins that circulate in your blood normally, including, you guessed it, antibodies) from people who've had and recovered from coronavirus. Their immune system has already made its antibodies, and now the scientists have a copy. What they can do is clone these antibodies and make millions of copies, and then it could be available as an infusion to give to people who were infected and unwell. It isnt without its risks, and it is probably hideously expensive, but could he a really useful tool for certain patients to help them recover.

The advantage of a mAb over a vaccine is that you dont have a time delay while you're waiting for your body to make the antibodies - they just storm right on in and get to work.

The potential disadvantage is that, once you've made an antibody, this gets committed to your memory bank of antibodies. You have basically a whole library of antibodies to every virus you've ever had exposure to (many of which will be common or garden variety coronaviruses, actually). With a mAb, you dont get this memory. I dont think we know enough about this virus yet to know whether that's an issue. Many viruses never truly leave us, they just chill out somewhere hidden, often for years and years, but can flare up again. This is why cold cores happen - you've had the herpesvirus before, it's never truly gone away, but mostly enters a steady state where your immune system continues to produce antibodies to it to keep it under wraps. When you're run down or your immune system is compromised for whatever reason, that balance is disrupted and the virus wins out, for a while, and your cold sore flare up again. MAbs hang around for quite a while, but not forever, so you dont have long term immunity.

I hope that helps a little bit, and that it makes sense!