After introducing how to use a drawing software and how to draw a picture step by step, I will share my favorite drawing materials that I found on Pixiv. They are all free to use. But some of them have different rules about how you are going to use these materials. I will mark out rules under the picture in the case of you can't read Japanese. Please read them carefully before you decided to use the picture.
This one is made by ポテ子. You can use it for fan arts, and ポテ子 didn't mention about commercial purposes. You are free to change the color, but you can't re-upload it.
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=29278371
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=29954183
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=29954183
They are both made by bambooo. You can use them for your own, school relates, animations, printed matters and commercial purposes. But you can't re-upload them, and use for illegal purposes and defamations.
This one is made by 雑音コア. You can use it for drawings, animations, fan art magazines. You don't have to tell the owner when you use it. You can change the shape whatever you like, but do not re-upload it.