And also if you want Japanese people to understand your Japanese writing then you need to learn kanjis too.
1.Use srs flashcards called 'Anki'
2. Download a vocab deck
3. Use it 10min a day
4. Learn words (combo kanji)
The HelloTalk app can be useful, even by finding honest friends in Japan to guide you and/or teach you. But, be cautious when meeting them.
Having some Japanese penpals will be rather beneficial after you can write to them in Japanese (complicated grammars and big words aren't necessary).