There are all sort of popular apps to learn Spanish, like Busuu, Memrise, Duolingo.. Anyone used multiple ones and could give their opinion on the best one, specifically for Spanish.
I don't know in spanish but Duolingo has helped me a lot learning portuguese. Take into account that spanish is not an easy language, a loot of different rules and pronunciation, so you might want to start listening to music in spanish, too
Duolingo is always a great option, but another good way is to watch films in Spanish. Pick a movie you've watched and are well acquainted with and watch it in Spanish. It should help improve your translation on the fly skills if you're already familiar with the script.
As others have said, Duolingo is a great option to start learning the language or brush up on your skills. Once you've got a decent grasp of the language, watching films and television can help with the pronunciation/flow and with vocabulary.
One thing that worked well for me personally was learning a lot of the basics with Duolingo. Moving on to reading some of my favorite old children's books to get a feel for how sentence structure is supposed to work for writing at a very basic level and moving on to higher level reading depending on how well you want to be able to read/write. Then watching a lot movies and television to understand how the more conversational aspects work.