Separate them with comma.
The maxResults parameter specifies the maximum number of results that should be included in the result set. This parameter works in conjunction with the start-index parameter to determine which results to return. For example, to request the second set of 10 results – i.e. results 11-20 – set the max-results parameter to 10 and the start-index parameter to 11. The default value of this parameter is 5, and the maximum value is 50. However, for displaying lists of videos, we recommend that you set the maxResults parameter to 10.
The start-index parameter specifies the index of the first matching result that should be included in the result set. This parameter uses a one-based index, meaning the first result is 1, the second result is 2 and so forth. This parameter works in conjunction with the max-results parameter to determine which results to return. For example, to request the second set of 10 results – i.e. results 11-20 – set the start-index parameter to 11 and the max-results parameter to 10.
The order parameter specifies the method that will be used to order resources in the API response. The default value is relevance.
Acceptable values are:
- date – Resources are sorted in reverse chronological order based on the date they were created.
- rating – Resources are sorted from highest to lowest rating.
- relevance – Resources are sorted based on their relevance to the search query. This is the default value for this parameter.
- title – Resources are sorted alphabetically by title.
- videoCount – Channels are sorted in descending order of their number of uploaded videos.
- viewCount – Resources are sorted from highest to lowest number of views. For live broadcasts, videos are sorted by number of concurrent viewers while the broadcasts are ongoing.
Note: A user's playlists feed is ordered by publication time beginning with the newest playlist. For a user's subscriptions feed, the default ordering is arbitrary.
Even more about query parameters here