Thanks for your question. I know MLA can be confusing for new users.
You can find shortcode examples in the “MLA Gallery Examples/Simple Examples” section of the Settings/Media Library Assistant Documentation tab. Here are two earlier support topics along similar lines:
Basic newbie where to start | WordPress.org
Confused Newbie | WordPress.org
You asked for “all images uploaded by a specific user“. You can use these parameters to do that:
Author, Author Name
You can query by author’s id or “Username”, the value used to log in to the site. In the database this is the “user_nicename” column (not the “display_name” column). For example, if you log in as “john” and your id is 2 you can code:
[mla_gallery author=2][mla_gallery author_name="john"]Multiple author ID values are allowed, but only one author name value can be entered.
You asked for “all images uploaded by users with a specific roll“. I regret that MLA does not have a solution for this case. The [mla_gallery] data selection parameters are based on the WordPress WP_Query – Class | Developer.WordPress.org class, which does not support this case.
You asked for “all images that contain the text ‘abc’ in the filename or Alternative Text“. You can use the “Keyword(s) Search” parameters for this application. Here is the shortcode for the example you gave:
[mla_gallery s="abc" mla_search_fields="file,alt-text"] I hope that gets you started with shortcodes for your application. I am marking this topic resolved, but please update it if you have problems or further questions regarding the above suggestions. Thanks for your interest in the plugin.