FreeType is a library that provides access to glyphs in font files. It scales the glyph images and their metrics to a requested size, and it rasterizes the glyph images to produce pixel or subpixel alpha coverage bitmaps.
Note that FreeType is not a text layout engine. You have to use higher-level libraries like HarfBuzz, Pango, or ICU for that.
Note also that FreeType does not perform alpha blending or compositing the resulting bitmaps or pixmaps by itself. Use your favourite graphics library (for example, Cairo or Skia) to further process FreeType's output.