A few years back, I wasted time on Duolingo trying to learn Spanish. I no longer do that and you shouldn’t. Here’s why it’s not effective and better alternatives.

1. Language is primarily an oral activity. The written language evolved later, primarily, for bureaucracy and tax collection. Any app that emphasizes the written aspect first is splitting your learning efforts.
2. The English and Spanish pronunciations are different. Duolingo leaves it as guesswork for you to figure out. In fact, despite doing 1000+ practice sessions (and ~100 lessons) on Duolingo, I could not figure out how was “hablé” supposed to be pronounced differently from “hable”.
3. Duolingo teaches you the same class of words in one lesson. For example, all animals in one lesson, all food items in another, and all family relatives’ names in another. And that’s confusing as hell since you start mixing them. Even worse is how these categories are fairly bookish and meaningless for a traveler, do you care about the grandmother (that’s Abuela!) of the tienda owner?
4. Duolingo won’t help you with conversational fluency. One of the most important activities a traveler has to do is ask the price for things/services he is going to buy. The numbers lessons are less important than learning the Spanish word for a grandmother!
5. Duolingo seems to teach some weird academic style. For example, in Spanish, you don’t say “Yo quiero” for “I want”, you say “Quiero”. Thanks to different verbs, the pronouns I/you/they are mostly implicit. Duolingo somehow doesn’t get that.
6. Duolingo doesn’t teach you any language transfer at all. For example, words like metal, ideal, and most words ending in -al are of Latin origin and can be used as-is in Spanish. Similarly, words ending with -tion can be made into Spanish by a simple transformation to “-cion”. So, “Application -> applicación”. I haven’t seen that in Duolingo either. Some consonant heavy word starts like Spain become Spanish by adding “e” to the beginning. And Spanish hates useless repeated alphabets, for example, “tennis -> tenis”. These rules save a lot of time. And Duolingo doesn’t teach you these insights at all.
7. Duolingo won’t tell you alternatives. For example, “I want it” -> “Yo quiero lo” or “Yo lo quiero” are both acceptable as word order is more flexible in Spanish than in English.

So, if not Duolingo then what? I would recommend LanguageTransfer an excellent resource for transferring English language rules to Spanish. And then Pimsleur. The actual audiobooks for Pimsleur are expensive, so, see if you can borrow them from your local library.