Low notes are usually forgotten or just plain ignored when learning vocal technique. I think that is very wrong, as seen that low notes also matter a lot, and well sung low notes sound beautiful. On the other hand, not being able to sing a healthy low note will seriously damage your vocal capabilities.
What to Do
Vocal exercises, start from your lowest note and move to the top.
Also, we tend to look downwards and drop our larynx (too much) when singing low notes. Try to keep your face straight up, and your larynx at the same place. If that is difficult for you, it helps to imagine the sound traveling/resonating more into the top of your head, or to sing upwards as you could call it. Usually the problem with low notes is in the fact that people place the sound too much in their mouth, and drop everything too much, which makes it all loose and uncontrollable.
Thirdly, low notes require more air than higher ones. That doesn’t mean you should blast everything you have into it, it just means that you should learn to take deeper breaths and support the note with more air if you are having problems with support.
If you feel confident, you can start singing songs. You could transpose any existing song so that its lowest note matches your lowest note. If you don’t feel like doing that, you could search for songs that include (lots of) low notes in their verses.
Don’t try to sing very high yet, focus on singing the low and midrange perfectly.