Railsドキュメント

params[:パラメータ名]

link_to 'ユーザ名', controller: 'users', action: 'show', id: =1

def show
    id = params[:id] # id = 1
end

form_for @user do |f|
    f.text_field :name
    f.text_area :body
end

def create
    name = params[:name]
    body =  params[:body]
end

xxx[]

xxx[aaa]