Whar tourist attractions should i see in barcelona,spain?

That Gaudi cathedral, the beach.

You can visit The Alhambra and Generalife Gardens, Granada, San Lorenzo de El Escorial,Costa del Sol Beaches of Spain and many more beautiful places of Spain

The Cathedral, Picasso Museum, Casa Milà and the other Gaudi buildings, La Sagrada Familia, Park Güell, La Rambla, Montjuïc especially the fountains, Museu Nacional d'Art de Catalunya

ask again after the pandemic

Sagrada Familia would be an obvious one. 

It rather depends on what you're interested in - maybe take a look at a guide book or city guide and plan what you want to see