Speaking in any language is all about imitating other people. You want to be able to speak like native speakers do. Before you can form your own correct sentences, you first need to see lots of similar ones in the language you are learning.
When you speak in your native language, you don't have to think about the grammar or the words you use. Correct sentences just come to you. In fact, your brain uses sentences you've already seen or heard. If you want to speak a foreign language fluently, you have to learn it the way you learned your native language - by massive input.
Reading and listening will help you develop language intuition. It's all about putting lots of correct sentences in your head. Then your brain can imitate them, producing similar sentences to express the meaning you want. When you read and listen a lot, paying attention to useful vocabulary, you will soon start to use new words and phrases in your speaking and writing. Not only that, you will develop language intuition. You will start to feel what sounds good and what sounds ugly - just as you do in your native language.
It may seem like you need more time to learn a language by reading and listening, as opposed to learning based on grammar rules. For example, to get a good feeling for the use of articles in English you need to read lots of sentences, analysing them closely. Wouldn't it be easier to read a unit on articles in a grammar book? Well, the problem is that it takes lots of time to build a sentence when you have to think of grammar rules. When you talk to someone, you don't have time for that. The input-based approach may seem to be more demanding, but it's the only way to achieve fluency.
Here you have some important websites where you can access to reading material and also exercises to train your comprehension: