hello all please help me I am new in CodeIgniter

hello all please help me I am new to CodeIgniter
Display products based on categories slug, subcategories URL, and child categories slug

my URL should be like this :

www.example.com/category_slug/ /* Related Item will show here / www.example.com/category_slug/subcategory_slug/ /

Related Item will show here 
    */

 www.example.com/category_slug/subcategory_slug/childcategory_slug

  /*

Related Item will show here 
    */

But I don't know how to this... My tables are like this

categories :

id,name,slug,photo

subcategories :

id,category_id,name,slug

childcategories :

id,subcategory_id,name,slug