Complex sentence: This happens when there is sufficient heating of an atmospheric layer to allow air in that layer to rise freely or, the air is dynamically lifted by upper level divergence, low level convergence, cold front, etc. to the LFC.
Split into simpler sentences: This happens when there is sufficient heating of an atmospheric layer to allow air in that layer to rise freely or, the air is dynamically lifted. This dynamic and forced lift can be from upper level divergence, low level convergence, cold front, etc. and brings air to the LFC.