I need a bit of advice. I have an e-commerce site on www.mydomain.com and I have now created a sub domain that will have a totally new store running on it (all installed any ready to go). I use prestashop and I want to point a category on www.mydomain.com to my new sub domain www.mydomain/sub.com. Can this be done? How would I do it?
If you want to make sub domain then it can't be possible as mydomain.com/sub.com but you can create it as sub.mydomain.com. If you are ready to make sub domain then log in into control panel of web hosting and then choose option as create sub domain. You sub domain facility available on your web hosting plan. I hope you can understand about sub domain.
either does not make sense or will confuse everyone or I'm not getting your question right
is a subdirectory
is a subdomain
In general context subdirectory and subdomain should behaves almost the same way. For SEO, the safe approach is to use subdirectory instead of subdomain e.g. http://www.whitefireseo.com/site-architecture/subdomain-or-subfolder-post-panda/360/ (there are a lot more preferences, feel free to do some searches)
The general directory structures on your server would be as follows for both subdirectory and subdomain case
As a result, what you need to do is the following 2 simple steps
Step 1: Create directory "sub" inside directory "mydomain.com" (this should be a breeze if you have access to cPanel or SFTP access to the directory "mydomain.com" and you have "write" permission to it
Step 2: Install a new prestashop website inside "mydomain.com/sub/"