Probably I am getting boring, but I can´t stress enough how important it is to learn as much German as possible BEFORE you come to Germany. If by some miracle I had had a chance to move back in time, that´s absolutely the first thing I would have done, as it not only makes getting a visa much easier, but it is a complete life-changer once you are there.
But how to do it, if there is not too much money to be spent on that or maybe no time to attend a course in a completely different part of the city? Well, sure, online, but where to start so you don´t drop it frustrated after just a few days? How to navigate in the jungle of websites offering German courses and most importantly - which ones are really for free?
No matter if you are an absolute beginner (you can´t think of any single German word you know) or you have already had some German classes before, I would definitely begin with duolingo. You can download it as a free app (that´s what I did) or use the duolingo website (I know some people who swear that on the website it´s better, but personally I have never used it). Then you have to select "your" language (not necessary your native language, but the one you understand really well, so it may be Arabic, Englisch, French, whatever you like), next you select that you want to learn German and you can choose if you want to start from zero or you would prefer to take a quiz assessing your level. There is where you start and little by little you get to know first very easy words and then some sentences.
The biggest adventages: you don´t need to wonder how to pronounce anything as the app reads every word for you and even asks you to read it aloud and record it in order to check if it really sounds like German. The tasks are easy, the graphic design nice for the eye and you really practise all skills: listening, speaking, reading and writing and it is 100% free, what means that you need to put up with some adds evey now and then, but it is not too bad. You are also frequently asked if you want to upgrade to an add-free (paid) version, but you don´t and that´s fine. I have been using the free version for years now and even though I have passed B1 already some time ago, I still learn a lot there.
Can you really learn a language there? I am sure you do and I personally know people who did using exclusively duolingo. First you get to know some funny sentences like "I have an apple" and "The cat likes the dog", but don´t lose trust in the whole! The courses are really carefully designed so you can achieve your language goal, keep doing!
Is there any way to accelerate your progress? What really works for me is to write down the new words and repeat them. After just a few days you will be impressed how many new words you have learnt! (I love counting them) Have them in your notebook and on post-its everywhere you can see them a lot. Additionally, I like taking pictures of my new words so that I can have a look at them in the situations where I have just my phone with me. Most people remember faster when they can see something, but make sure you repeat the words aloud, so you get familiar with the way they sound. Learn the whole sentences (that´s very useful especially in the beginning when you are never sure about the right word order or endings) and don´t be afarid to make your own sentences similar to the one you are learning. If you are learning "I have an apple", think how to say "I have a cat", "I have a dog", "I have a banana", "I have a sister" etc.
The only thing I sometimes miss about the duolingo is grammar. You will find there some basic explanations when you make a mistake, but sometimes you just want to know why this is right and the other wrong. In this case I would recommend the Passau courses "Deutsch - Aber Hallo!" You can easily find them online just writing "Deutsch aber hallo pdf a1" (or a2, b1, b2, they have pdf exercises till the Level C2). If you need to check, if your answers are right, look online for "Deutsch aber hallo a1 answers pdf". This is really a great collection of grammar exercises for free.
How many words you need to start speaking? I would say at least 1000 for a very basic communication and about 2500 to pass the B1 exam. It seems really a lot, but every big journey starts with the first step, take a challenge, start learning, Count your words and you will be surprised how fast they add on. Good luck!