Ruby on Rails - showing all instances in a view, with specific column value, returned by other table column

First, my schema looks like this:

create_table "categories", force: :cascade do |t|
t.text     "name"
t.text     "slug"
end

create_table "fields", force: :cascade do |t|
t.integer  "order"
t.string   "title"
t.text     "tipo"
t.text     "values"
t.integer  "sub_category_id"
end
add_index "fields", ["sub_category_id"], name: "index_fields_on_sub_category_id"

create_table "sub_categories", force: :cascade do |t|
t.integer  "category_id"
t.text     "name"
t.text     "slug"
end
add_index "sub_categories", ["category_id"], name: "index_sub_categories_on_category_id"

This is my schema, a category has many sub_categories, and a sub_category has many fields. Im trying to generate a view which contains all fields of a specific sub_category, i've already passed the sub_category.id to this view, but thats all i could do.

Its not that difficult i imagine, but im a begginer on rails. How can i do it? The routes are also a problem, since i have to create a new controller function. But the route generated by my application already looks like this: "/sub_categories/mysubcategory56/visualizeform?sub_category=56"