To access the 'Product Details', from the store dashboard go to:
> Products > All Products

From within this page find the 'Product' you'd like to 'Edit' by either scrolling through or searching for it via the search box in the top right:

Once you've found the product you'd like to edit, hover over the product with your cursor and click 'Edit':

When the next page opens up, scroll right the way down to the heading 'Product Details':

In the 'General' tab the 'Help' guide on the right explains what the different 'Product type' means. As for the other features in this tab, AliExpress imports all the product data here and so is not that relevant.
One below the 'General' tab is the 'Attributes' tab - if your product contains a few different colours, sizes etc, this is where can you create them:

To add an attribute, click 'Add attribute':

From there you can 'Name', 'Add values' and 'Images' of the different attributes the product contains. Here's an example of a USB cable with multiple colours and lengths:

To switch off an attribute for the time being, uncheck its corresponding tick box. To permanently delete the attribute, click its corresponding cross (X):

One below the 'Attributes' tab is the 'Variations' tab - this is where you set prices for each of the products attributes:

To add a variation, click 'Add variation', or to add all possible variations click 'Add all possible variations':

From there you can select the products 'Attributes' (colours and lengths in this case), edit 'Cost Price' (how much you pay for it on AliExpress) 'Regular Price', 'Sale Price' and 'Quantity'. To switch off a variation for the time being uncheck its corresponding tick box, to permanently delete the variation click its corresponding cross (X):

Below the 'Variations' tab is the 'Specifications' tab - this where all the products key information is stored:

As you can, the information formulated above is shown below under the 'Specifications' tab on the product page:

To add additional 'Specifications', click 'Add row':

The next tab down is 'Supplier' - these are the suppliers details imported from AliExpress (should not be changed):

*Details such as the 'Store rating', 'Cost price' and 'Stock level' update automatically and shouldn't be altered*
The second from last tab is 'Gallery' - contained within are all the photos of that specific product:

The order of the photos shown above correspond to the order of the photos on the product page:

To alter the order of the images hover your cursor over the icon in the top left of a photo, then drag and drop it into your desired position:

To add more images, simply click 'Add image' at the bottom.
The final tab is 'Reviews' - inside contains the settings and criteria for publishing reviews for that individual product:

*Use the 'Help' guide on the right for explanations*
(*Don't forget to click 'Update' at the top of the page after making alterations*)