Thaís, my corrections and changes to your text are shown below:
First of all/Firstly, in my opinion, love is the most precious thing in life. There are many kinds of love, brotherly love, family love, and love between couples.
By the way, we should value people's love, bearing it in mind that respect is one of the fundamentals of love.
Nowadays, *many people don't know how to love and respect others. This may cause many cases of violence, which is very bad.
Everybody needs to build more love in their hearts. This can be This is how many kinds of problems start.
Therefore, we should share our love with other people. This is very important.
Finally, without love everyone would be lost, because only love can save the world.
*Try not to generalise.