HelloTalk is good to practice conversation, but not nor learning grammar, especially for a beginner. In fact, without basic grammar, you would find yourself unable to express basically anything on HelloTalk. If you want to have spoken conversations, it’s harder to find a good partner and agreeing on a schedule can be a pain.
If you don’t have much free time and you don’t know a lot of grammar, I’d recommend you take a look at Pimsleur’s course. It’s obviously not as good as talking to natives regularly or taking a proper course, but you can do the 30 minute lessons on your commute, or while you’re exercising or cooking or whatever. I do them while I’m driving to work, so it doesn’t require me to give up any more of my (already scarce) spare time. They start at the very beginning and no previous knowledge is assumed. The lessons introduce grammar points and vocabulary a bit too slowly if you’re already familiar, but you are constantly prompted to repeat after the speakers and to participate at the dialogues. All dialogues are acted out at native speaker speed, so your listening and speaking will definitely improve.
Your can read about it in more detail here: