To start / stop ad groups within a campaign, you can first
fetch a list of all ad groups in a campaign
and for each ad group,
update the status of the ad group to paused (examples are implemented in Java programming language, similar code snippets are available in other
client libraries as well). For performing AdWords API operations without using one of our
client libraries, please refer to
this guide. Also, you would need to
create or link an AdWords client account to your AdWords manager account to be able to perform regular operations. Manager accounts are used to manager other accounts and do not have the capability to run campaigns/ads.
Please feel free to revert in case you have more questions.