A lot of people are frustrated to find that, after spending many hours on Duolingo, classes, anime or whatever, they understand a lot but are still unable to have basic conversations with native speakers. If that's you, this article will help you diagnose what the reason is and also suggest what you can do in order to fix the issue.
Let's do a test: Stand up and walk once across your home and back. Imagine that you're meeting an old friend on the street. Say "Hey!! How are you? Long time no see! How have you been?" in your target language.
=> If this came out spontaneously and you are also able to use it spontaneously in real life situations, your issue is probably higher-level language. Solution: whenever you're unable to interact as you wish you could, write down (or make a quick voice note) the phrases you're missing and then study these and similar phrases once you're back home, ideally with a tutor who can also do situation practice with you.
=> If this came out spontaneously but you're unable to react like this in real life situations, your issue is probably inhibition. Look up general tips for shy people. Also, remind yourself that almost everyone is happy to hear that an English speaker is making an effort to learn their native language - in the case of less commonly studied languages like Chinese or Modern Greek, people are happy to hear even a "Hello! How are you?" - so you should make them happy as often as possible, even if you're not yet fully fluent.
If you had a lot of trouble saying these basic phrases, do another test: take pencil and paper and write down "It's such a nice day! What are you doing here?" in your target language. Then try to pronounce it naturally.
=> If you were able to write this without much deliberation and also pronounced it well, the problem is at the level of speaking practice. Your brain is not in the habit of calling up words in conversation and you may also not have enough chunks. Solution: book some lessons (e.g. through the "Find a Teacher" menu item) or language exchanges which will be 100% dedicated to conversation. Don't work with textbook dialogs but try to have natural conversations with your tutor. They will be slow and clumsy at the beginning but get much better after a few hours already, especially if you revisit the same topics. When not taking lessons, engage in self-talk or work out language islands.
=> If you were able to write this without much deliberation but the pronunciation was awkward, your tongue is not yet in the habit of producing the language. Every language has its own kind of tongue gymnastics. Even after you can do all the basic vowels and consonants, it still takes some practice to have the transitions come naturally to your tongue. Solution: whenever you see a word or phrase, say it out loud. Use audio-heavy materials (e.g. Michel Thomas, stories on this site's Reading Tool with accompanying audio, Youtube videos with matching target-language transcripts) and imitate the speaker as often as possible. Don't whisper, speak loudly and proudly. If you're finding it difficult to match the native speaker, take a tiny extract, slow it down to 80% speed or less, work until you can imitate that, then gradually speed it up to full speed.
=> If you hesitated a lot on the writing, the problem is vocabulary/phrases. You may even know a lot of vocabulary but not the right kind. Maybe you learned a list of words for animals or fruit but you haven't yet learned phrases like the above - a common problem when using apps rather than actual language courses. (It's much easier to produce an app that teaches you word lists rather than to produce a course that teaches you how to speak, hence almost all apps teach word lists and nothing else.) Change methods. Browse before you buy and look for a course that contains the kind of dialogs that you'd like to be able to engage in, for example Benny Lewis' "Language Hacking" language courses, Teach Yourself "Complete" language courses, Michel Thomas, Assimil "With ease" courses, my own "Systematic Approach" decks for Anki... Supplement with a tutor who can teach you me-language, that is, the kind of phrases and dialogs that are uniquely you, to talk about your hobbies, your situation and so on.
Speaking is not magic! But neither can you expect to magically develop speaking ability while only doing passive (listening or reading) activities. Read a lot when you want to develop the ability to read (and grow your vocabulary), listen a lot when you want to develop the ability to listen, speak a lot when you want to develop the ability to speak. Every muscle has to be trained separately, and this guide allows you to identify which of your speaking "muscles" is weakest. Good luck!