Hey why are you putting '=' sign in first line. <% %> are used for telling rails that string under this is ruby code,evaluate it. Where as <%= %> this tells rails that string in these tags is in ruby, evaluate it and print the result in html file too.
Hence try to inspect your code you are writing
<%= @todo_array.each do |t| %>
while this line is only for iterating over @todo_array hence we wont be in need to print that line. So final code should be
<% @todo_array.each do |t| %>
<%= puts t %>
<% end %>
