At the beginning, you will have to chose 5 villagers to take to Isola. You should chose 1 male, 1 female, 1 female with a baby,1 child(age 13 and younger preferably around age 6 or 7) and another person of your choice. The baby with the woman will not count as your last person. You still will have more than 5 people but only because of woman with babies.
To get started, you should create a fire. First, drag an adult villager(ages 14+) to the pile of grass left of the wooden stairs.They will pick some grass up and place it on the black spot just below the grass. Don't worry, the grass is unlimited. Next, drag another adult villager to the pile of wood left of the grass. They will pick up some wood and bring it to the black spot. The wood is also unlimited. Drag an adult to the black spot which should now have both grass and wood on it. The adult will start a fire. Throughout the game, the fire will come in handy. After several hours in the game have passed, the fire will go out. All you have to do to relight it is to do what you did with your first fire.
You will need food. For now you have to use mushrooms and berries. To get mushrooms you have to see them appear. They will usually have blinking sparkles around them. They are almost always brown but sometimes the red rare ones appear (the red ones come out more often in the rain). The mushrooms appear for only about 15-20 seconds, so you have to act quick. Pause the game by pressing the space bar. Then, grab a child and put it on the mushroom. The child will bring it to the food bin. To get berries, you need an adult. Go to detail and find an adult that has no dislikes of any kinds of foods or plants. Set their skill to "farmer" by clicking in the box right of the skill "farmer." Once that is done, exit detail, grab the villager, and drag them to the purple berry bush left of the bridge leading to the science lab. The villager will pick some berries, bring them to the food bin, and hopefully continue collecting berries. If they stop, drag them back to the food bin. It is normal for them to keep stopping at the beginning.
You will need tech points to master many things in the future. To become a scientist, go to detail and set an adult as a scientist. This villager should NOT dislike any type of science or things to do with science. Exit Detail. Drag the villager to the table in the science lab above the bridge. They will start researching and may stop. Just drag them back to the table if they do. If you see any flute heads or items that are not usually where they are now, pause the game and drag a child to it. When you un-pause the game, the child will bring it to the science lab, flute head area, or to the mausoleum. If you go to the tide pool at the very bottom right corner of the island, you may find fish scales. You will need a child for this one. Drop the child on it. The child will bring the scale to the fish statue to the right of the tide pool.
Building allows you to increase your population. To become a builder go to detail and set your villager to be a builder. Exit detail and drag the hut parts wherever you want your hut to be. (The hut parts look like a bunch of wood in piles). Drag your builder to the hut parts. This villager will start building by going back and forth to the wood pile and back to the hut. It may take a few tries to keep with the building and not wander off. Once you have finished the hut, you can build the "Love Hut."
Health is very important for survival. To avoid becoming sick, make sure that you have enough food and regularly go to detail and check for health. Healthy and Weak are OK, but sick is a bad sign. Don't worry, there is a simple solution to become healthy again. Take an adult villager and go to detail and set the villager on healing. Exit detail and place the healer on the sick person. It might take a few tries, but the healer should heal the person. This person will become a better healer.
Parenting is the key to life. To make a woman have a baby, you must have the love hut built. When the love hut is built, drag a woman who is not too good at any skills(so that it won't matter as much when she can't work)with any man. They will "embrace" and "go indoors." When they come out either the woman will have a baby in her arms or will continue working on her daily job. A quick and easy way to tell if a woman will have a baby is to when they go indoors, look at the population at the top of the screen. If it is higher, the woman is having a baby. If not, she is not. To avoid having to wait for them to go indoors, you can drag a man to a woman and then check the population. If it hasn't changed, try again and again until she has a baby. Women can have 1,2, or 3 babies at the same time. They can not work while having a baby in their arms. During the period with their babies, woman will show them around, change them, wash them, and do a lot of other things with them.
I wish you all of luck to save the Tree of Life. With this guidance, you should be on your way to saving the tree.