You could just use jellyfin as backend and build another or even better frontend for it. AFAIK there is a vue frontend for it as an example.

https://github.com/jellyfin/jellyfin

I don’t intend to sound mean, but to be frank, you’re far off ever starting such a website. Given your knowledge, I’d also recommend staying away from such a project until you have more experience in the relevant fields. The reason for this is that there’s a number of intricacies you need to be careful of when building a piracy streaming platform (both technicalities, logistics, and what sort of negative attention you could bring), which you probably won’t pick up if this is your first project.

Having said that, I’d start at looking at back-end dev - this will give you a greater amount of knowledge. After that, you can decide how to approach the problem, e.g. if you’re scraping another website, you’ll need some way of pulling data on the back end (either on the fly, or via some periodic task).
Another aspect to consider would be the logistics, e.g. if you want to host the video files yourself, what sort of bandwidth would be necessary for a certain degree of traffic.

Then assuming you can solve all the technical problems, next to consider is maintenance, promotion and funding.

They most likely fetch the torrents for the episodes via RSS feeds (on Nyaa for example) and then upload the video to a 3rd party video hosting service and then link it back in their own player. Almost no site (except the licenced ones) host the videos by themselves.

I don’t want to sound mean and defeatist, but steaming service is very expensive to run due to the sheer amount of bandwidth and storage cost required. You can host standard website for free these days, but video hosting is another story.

Consider a standard 1080p video stream @ 16mbps. If your server has 1gbps bandwidth, you can only serve 62 people at the same time. You’re going to need more and more bandwidth as your users grow or they’ll get irritated and leave because your servers don’t have enough bandwidth to serve videos to all of them (lots of buffering and timeouts).

So how much will those bandwidth cost you? If you plan to host them in a cloud provider, you should know that they’ll usually charge by the amount of egress traffics you consume. If you maxed out a 1gbps link for a month in an AWS server, Amazon will charge you around $0.1 per GB, which means you’ll get a hefty $32,400 at the end of the month for delivering 324TB of traffics.

Now AWS is literally the most expensive provider in term of bandwidth, so you might want to use a provider that provides unmetered billing. This usually means traditional colocation service where you buy your own physical servers and only pay for electricity and internet, or renting out dedicated servers which will cost a lot upfront but ended up being cheaper than pay as you go cloud providers. But you’ll still looking to pay thousands $ each months to pay for the bandwidth.

Some pirate streaming sites cheats by uploading their videos into various cloud file storage such as Google drive and playing cat and mouse by constantly creating a new account and reuploading their videos when when their account for banned for violating tos. You might be tempted to go that route as well, but considering how you’re already sweating at the prospect of finding and uploading all anime files yourself, constantly creating a new cloud storage account and constantly reuploading your anime files doesn’t sound really great, right? Some pirate streaming sites literally have full time staff doing this stuff all day, constantly keeping up with new anime release, downloading them released schene torrents or ripping them out from Crunchyroll, then uploading to a cloud storage account or other video hosting services (and reuploading again if it were taken down due to tos violation).

I think this project is way too big for you right now, but pretty fun to think about especially the logistics part.