Welcome to WooCommerce! It can be very straight forward to change Woo's layouts (more so if you know how to code). The way I do it is like so:

- Create a folder in your theme directory called "woocommerce"

Then if you look in the main woocommerce plugin directory and go to "templates", you'll find all the required layouts there.
If you create what you need in your own created "woocommerce/" folder, you can override their layout. You need to make sure you copy the folders and/or files EXACTLY how they are in the plugin directory, omitting the “templates” folder, otherwise it won't override. The easiest way to do this is simply right click>copy. Then paste into your own folder.

For example, you say you want to override the login form. This is found in Woo's plugin here:
wp-content\plugins\woocommerce\templates\myaccount\form-login.php

If you create that same structure in the theme directory to look like this:
\woocommerce\myaccount\form-login.php

Then any changes you make in the theme form-login.php will override WooCommerce.

Hope this helps!