twitter clone - trying to show the users username next to their tweet on tweets index - devise

I'm trying to create a twitter clone. I'm at the point where a user can post a tweet and it shows the content and the time it was posted. However i want it so the username is also next to the tweet of whoever tweeted it. i'm unsure how to do this as the error is currently 'Couldn't find User without an ID' in my tweet controller create method. I'm also not sure of the syntax to display the username in index.html.erb. thanks.

class TweetsController < ApplicationController

  def index
    @tweets = Tweet.all.order("created_at DESC")
    @tweet = Tweet.new
    # @user = User.find(params[:id])
  end

  def show
    @tweet = Tweet.find(params[:id])
  end

  def new
    # @tweet = Tweet.new
  end

  def create
    @user = User.find(params[:id])
    @tweet = Tweet.new(tweet_params)
    @tweet.user = @user
    if @tweet.save
    redirect_to tweets_path
  end
  end

  def edit
    @tweet = Tweet.find(params[:id])
  end

  def update
    @tweet = Tweet.find(params[:id])
    @tweet.update(tweet_params)
    redirect_to tweets_path
  end

  private
  def tweet_params
    params.require(:tweet).permit(:user_id,:content)
  end
end

<h1>TWEETS</h1>

<%# @users.each do |user| %>
<%#= user.username %>
<%# end %>

<%= simple_form_for @tweet, id: "form-submit" do |f| %>
   <%= f.input :content, label: "Tweet" %>
   <%= f.button :submit, class: "btn btn-danger" %>
   <% end %>

   <br>

<% @tweets.each do |tweet|  %>
  <ul>
    <li>
      <%= tweet.created_at.strftime("%B %d %Y, %l:%M%P") %> <br>
      <%= tweet.content %>
      <%#= tweet.user.username %>
    <%#= tweet.user.username %>
    </li>
  </ul>
<% end %>