I live in a warm climate. Is there any variety of cabbage that will do well here?
This article has several great suggestions for both varieties to grow and tips for help to grow cabbage in areas with warm weather:
https://www.gardeningknowhow.com/edible/vegetables/cabbage/growing-cabbage.htm
How can I prevent the cabbage root fly? Is there any insecticide to be had? Also, what is best for clay soil?
This article will help with this: https://www.gardeningknowhow.com/edible/vegetables/cabbage/control-cabbage-maggot.htm
My cabbage plants are growing up instead of round. Same with the lettuce. What am I doing wrong?
This sounds like it is a bit too warm for them and they are starting to bolt. Try to keep the soil cooler, this will help. To help keep the soil cooler, mulch heavily around the roots and keep the plants well watered.
I have cabbage growing. It has big healthy green leaves but no head. When should it develop a head, or do I just pinch off the large green leaves? Also, my broccoli is about 6 inches high. The pimples (I call them pimples) are small and light in color. Do you think it will develop into something to eat? I am a new planter. . .thanks.
Cabbage takes a bit to develop a head, just give it some time and do not trim the leaves off.
Broccoli is prone to bolting. If a head is forming, that is a good sign, but just take some steps to keep it from flowering. This article will help:
https://www.gardeningknowhow.com/edible/vegetables/broccoli/bolting-broccoli-growing-broccoli-in-hot-weather.htm
When I start growing plants from seeds, why does it take forever for the plants to get big enough to set out? Things like cabbage seeds come up way faster and get bigger before tomato plants, head lettuce, and other things. Why is it like that?
It is just the nature of the seeds. Some grow faster than others. Judging from your examples, I would guess you did not use a heat source to help germinate (which is fine) and cabbage germinates faster and better at a lower temp than, say, tomatoes.
My cabbage looks limp and frail. How do I keep it alive?
It may be going into transplant shock. This article will help:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm
I need to know how to start preparing the soil and how the beds are going to look. What is the height and all to make the bed ready for good cabbage planting in summer in Africa?
These articles will help you:
https://www.gardeningknowhow.com/edible/vegetables/vgen/vegetable-garden-soil.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-vegetable-gardens.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/how-to-plant-a-vegetable-garden.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/starting-a-vegetable-garden.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/vegetable-gardening-for-beginners.htm
https://www.gardeningknowhow.com/edible/vegetables/cabbage/growing-cabbage.htm