And can you tell me the meanings of shapes and colour?

That would really depend on the artist. Many abstract painters do not put meaning into each stroke, color or shape. Viewers project meaning onto them, at times even seeing shapes the artist did not intend. Look into historians like Clement Greenberg for more info about abstract painting.

I am an abstract painter and I think the painting paints itself. I never think of what the outcome is going to be. It just evolves onto the canvas. Shapes are a basic primitive meaning. it is also a structural placement.
Even if you don't think of what you are painting the structure has to be complete. Your eyes are trained to pick colors and assemble them in a pattern. If you see a painting that doesn't look right, then look closer at the placement of colors on the painting. There will be an area you eye seems to be driven to if the painting is like this. That is the area of the painting that isn't finished, or the color placement if off.
Color is also a primitive aspect as this is also found in nature. The blue sky the green grass are all paintings.
To answer "the every stroke and color have meaning", this would depend greatly on the artist. Some I know have to imagine every stroke before the pick up a brush. Others think as they paint. I usually paint till the painting tells me its done.