Here's a few details from Notes Plus' tools (images followed by short description).
The main toolbar has 4 boxes, from the 7 tools you pick your 4 favorites.
The zoombox toolbar has 3 boxes for your favorite tools, and 3 for your favorite styles.
Please note that you can delete something by just draw a stroke through your text, and select something by drawing a circle around it. So the Eraser and Selection rectangle aren't that important.
Tap the tool preview to open the Style sheet. Ballpoint, fountain pen, calligraphy pen and brush are the possibilities. Each one has colour, thickness, viscosity and eventually a fill. Save your settings as a favorite by tapping the star in the top right corner.
Pick a colour from the colour wheel and adjust the opacity.
Another way to specify your colour of preference.
The fill option lets you write in hollow body characters. Here, the fill colour is set to white - can be anything though.
The style sheet for calligraphy.
Once you activate the Text tool, you start typing at the top left of the page. There's an option to extend your keyboard to show some extra's like a date and a time stamp, TAB...
A two finger tap brings up a menu from which you can create a text box anywhere on the page.
I'll let you do the comparison to Notability, after all my thread is about Notes Plus

Don't hesitate to ask more if needed!