Go to your Joomla admin page. Now go to extensions, module manager. Now on that page, click on new. Now select login button and click on next. Now type the name and set the position, it depends on the template you use like if you have the help file of that template, you can figure it out by checking that but many free template does not contain the help file. So for now, set the position left and click on save. You can arrange the order of your modules just by clicking the up icon or just by entering the number. Now login page will appear in every page but if you want to show it only on the home page then under the menu assignment, click on login module again, select the "select menu items", click on home and then save it. Now it will appear only on the home page.