I have watched the videos and here is my interpretation/summary of what they are showing.
Row 1Left: A Marchantia plant is shown growing. This is a great example of flabellate dichotomous branching. The apex divides into two (dichotomous) branches that are equal in size and it occurs in a fan-like (flabellate) shape, all in a single flattened plane.
Right: Watch gemmae grow inside of a gemmae cup. Gemmae are small discs of plant tissue. They are located inside a splash cup. When raindrops fall into the cup they dislodge the gemmae and splash them out onto the soil. One gemmae can grow into an entirely new Marchantia plant. This is a from of asexual reproduction.
Row 2 - All about spermLeft: A drop of water is added to the surface of an antheridiophore. This is an umbrella shaped structure that houses the antheridia, the organs that produce sperm. When the water is added some cloudy areas appear in the liquid.
Middle: This is a zoomed in shot of the previous video. Sperm are being released from a pore in the surface of the antheridiophore. The antheridia are located in cavities below the surface of the plant.
Right: Even more zoomed in. Aren't microscopes fabulous! Here you can see the flagellated sperm swimming in a twirly, spiral dance.
My summaries of Rows 3 & 4 are below the fold.
Row 3 - More sperm and closer to fertilizationLeft: Sperm are shown swimming toward the neck of an archegonium, the organ that produces and contains a single egg.
Right: Then the sperm are shown swimming into the neck of the archegonium toward the egg. After fertilization a sporophyte (2n, diploid) is produced.
Row 4Left: These umbrella-shaped structures growing out of the thallus are archegoniaphores. They house the archegonia, the organs that produce and contain eggs.
Middle: Unfortunately the link to this video does not work. The image is of an archegoniaphore whose archegonia have undergone fertilization and sporophytes have been produced. The yellow powder coming out of the archegoniaphores is spores.
Right: This video shows spores being released from the sporophytes on the archegoniaphores. The umbrella-tops of the archegoniaphores have flipped up, as though they were blown inside out in a strong wind. All of the particles blowing around in the breeze are spores. Each of these spores can land and grow into an entire new Marchantia plant.