Confusion over trains and the Tube in London travel

The tube operates in London and immediate environs--like the subway in NYC. It doesn't go as far as Oxford, which is about 60 miles from London. For that you'll need a train or an inter-city bus ("coach" in England). You may need to use the tube or a city bus to get to the appropriate train or bus station in London for the trip to Oxford.

The tube is the underground system for Greater London - it doesn't go anywhere near Oxford.
From where you are you need to get to a train station to get a normal train to Oxford. Normally the quickest way would be a direct train from Paddington station. On 28th May there will still be a problem between Didcot and Oxford which means a change. You can either get a direct train from Marylebone station or take a train from Paddington and then a bus from Dicot to Oxford. The bus is part of the service to get you round a viaduct which is being repaired, so in both options you only need one ticket. Either way takes about 90 minutes.
To further confuse you there is also a coach service called the Oxford Tube from London to Oxford. That takes about 2 hours 15 minutes but the timing can be affected by traffic.

Don’t understand what is confusing about it. Get an Oxford Tube coach from Buckingham Palace Rd every 15 minutes 24/7.

I haven't made the journey from London to Oxford. I have researched it a bit.

As to trains, you can find schedule/ticket information at the National Rail website: https://www.nationalrail.co.uk/. That shows direct trains running to Oxford from Marylebone rail station in London, and trains to Oxford with 1 change, leaving from Paddington rail station.

I would take the Tube from the Tube station nearest my hotel, to the appropriate rail station, then the train to Oxford.

Another option, not much discussed here, is a coach [bus] service between London and Oxford. I've bookmarked it as something to look into. It's called the Oxford Tube - which is rather confusing, LOL, because of course it's not a train or Tube at all. Details are at https://www.oxfordtube.com/ . It runs in both directions several times a day and is inexpensive - full fare round trip is £18. I've noted it because one of its London stops is so near my London hotel. Their website has detailed information on the stops in Oxford and in London.

EDITED to add: Snap! I cross-posted with Nick, much the same information.

Both train routes - from Paddington or from Marylebone will take you 1 1/2 hours-
Marylebone is straight through, Paddington is change to rail replacement bus at Didcot Parkway due to the ongoing bridge repair works.
Assuming you are on the north side of Kensington Gardens you would take the Central Line tube from Queensway or Lancaster Gate 1 or 2 stops respectively changing there to the District/Circle line 2 stops to Paddington (or 1/2 stops the other way to Bond Street, then Elizabeth line 1 stop to Paddington).
For Marylebone it is 3 stops from Queensway/2 stops from Lancaster Gate to Oxford Circus, change onto the Bakerloo line 3 stops to Marylebone.
There is little in it time wise. It's personal preference.
If you are on the south side of the gardens it's clearly Paddington- Bus 9 or 10 west to High Street Kensington station, then 3 stops on the District/Circle Line to Paddington.

The other option is to catch the Oxford Tube coach service every 12 to 15 minutes from Stop N at Notting Hill Gate Station, Bayswater Road- https://www.google.co.uk/maps/place/51%C2%B030'34.6%22N+0%C2%B011'34.7%22W/@51.50961,-0.1951687,17z/data=!3m1!4b1!4m4!3m3!8m2!3d51.50961!4d-0.19298?hl=en
On a Sunday that only takes 1 hour 40 minutes, so not much slower than the train.

Just to add that you might find that an intermediate stop on the Oxford Tube is closer to where you are staying than staying on to the bus station. Or for that matter a stop on the X33/X2 from Didcot.

The confusion is because

• the Underground has the nickname of the "Tube"
• there is a coach service called the Oxford Tube

Either use the "Oxford Tube" coach - can't recall its exact route but do know it has a stop near Marble Arch. If that's your nearest just use the Underground Central line to Nottinghill Gate

Otherwise take a train to either Paddington or Marylebone, then the Underground lines from there.

Tricky to be more specific as Kensington is covered by a few options in terms of Underground stations and lines