I recommend to you the following Apps in order to improve your German
LANGSAM GESPROCHENE NACHRICHTEN
VOKABELN LERNEN mit Duolingo
BOOK (if your native language is English)
If you really just need English worded grammar explanations, there are a ton of these resources online. This is the best and most comprehensive website for German grammar explained in English. She has bunch of exercises and the answer keys to go with them. It’s really brilliant: http://www.nthuleen.com/teach/grammar.html .
Also “Learn German with Jenny” on YouTube is very nice. She has some really nice video tutorials for learning German. Here is her website that also includes exercises: http://germanwithjenny.com/.
Beyond this, I’d also check Yabla which is great for audio visual content for learning German: https://german.yabla.com/
I like the following books to prepare for the test
• Prüfungstraining DaF: A2 – telc Deutsch A2: Dieter Maenner
• So geht’s noch besser zum Goethe-/ÖSD-Zertifikat B1: Ignatiadou-Schein…
• Mit Erfolg zu telc Deutsch B2: Zertifikat Deutsch Plus. Hans-Jürgen Hantschel
As well, I also do highly recommend the practice tests on their web pages