The lLast weekend I traveled to the beach.

Or "this last weekend"

There is a hotel inat the beach, I haved a reservation in itthere.¶
OR: I had a reservation at a hotel at the beach.

I'd say the second sentence personally, it sounds more natural to me. But both work well!

I’m checked in early at the hotel early and enjoyed the landscape.

The beach is near the hotel, during. In the morning I was takingtook photos, atin the afternoon I walked on the beach,. I wanted to swinm, but I saw a lot of jellyfish.

My weekend inat the beach

The lLast weekend I traveled to the beach.

This past weekend is another another way to say it but we definitely don't use "the"

There is a hotel in the beach, I have a reservation in it.

Or i have a reservation in/at a hotel at the beach

At the beach means "in a beach town/very close to the beach"

If you say a hotel ON the beach, it means literally on the beach. You can see the water from the hotel etc

I’m will check in at the hotel early and enjoy the landscape.

We would probably use scenery rather than landscape

The beach is near the hotel,. during the morning I was taking photos, at. In the afternoon afternoon I walked on the beach,. I wanted to swinm, but I saw a lot of jellyfish.

Nice job on this one.

My weekend inat the beach

at instead of in is more natural here.

The last weekend I traveledwent to the beach.

American english typically doesn't use 'travel' for casual or more ordinary circumstances.

There is a hotel inat the beach, I haved a reservation in it.

at over in again, as well as past tense

I’m checked in ato the hotel early and enjoyed the landscape.

Past tense required, checked into versus checked in at.

The beach is near the hotel, d. During the morning I was takingtook photos, atnd in the afternoon I walked on the beach, I wanted to swin, but I saw a lots of jellyfish.

Style updates as well as word choice.

My weekend inat the beach

The lLast weekend I traveled to the beach.

I think it sounds a bit more natural to say 'I went to the beach', unless you specifically mean to say you travelled quite far to get there or so.

There is a hotel in the beach, I haved a reservation in itat the hotel there.

It's better to stick to one tense when telling a story. Also since you already said you went to the beach, you can simply refer to it again without repeating 'the beach'. You could also say you had a reservation at one of the hotels there, if there are multiples hotels at the beach.

I’m checked in early at the hotel early and enjoyed the landscape.

Same as above, better to stick to one tense

The beach iwas near the hotel, d. During the morning I was takingtook photos, atnd in the afternoon I walked on the beach,. I wanted to swinm (but couldn't?), but I saw a lot of jellyfish.

It's now unclear if you swam or not. You do start the second part of the sentence with but, which implies that even though you didn't swim you managed to see jellyfish.