Complex sentence: After transcription, the rRNAs associate with the ribosomal proteins, forming the two types of ribosomal subunits (large and small) than will later assemble in the cytosol to make a functioning ribosome.
Split into simpler sentences: After transcription, the rRNAs associate with the ribosomal proteins, forming the two types of ribosomal subunits (large and small). These will later assemble in the cytosol to make a functioning ribosome.