@lollipop - as what is mentioned above, running a hard cable is the best solution, but it does depend on your circumstances, e.g. able to run pysical cables from the router directly out to the shed / are you able to wire it up yourself or know someone who can (MUCH easier than you think) / purchasing the correct equipment / etc.
There isn't much to it if you want to put in a pysical cable - if you have wired a plug in the past, it's not a huge step up from that to wiring a network cable. It should be at least
cat5e (can support speeds up to 1Gb), but if you are doing it, then use
cat6 / cat7 (to future proof it). A simple crimping set like
this one is a must have, some
connectors /
network port for the wall,
plug. There is SO much info online on how to do this and your situation, there are multiple ways to do it.
All the above might be double dutch to you or maybe not - but honestly, there isn't much to it. Loads of people on this site will have experience and can guide you if you need help. The hardest part will be getting a cable from the router to the shed. Once you have a cable out there, then you can set up multiple connections for a computer / TV / smart devices etc.
The links I've referenced above as just examples and a place I've purchased in the past from when I was doing it in my own home - I would highly recommend them - very satisfied customer.
Edit - might be better purchasing an outdoor type cable like this
cat6