"吃进肚子里"是这个短语最开始的意思.也是最literal (字面上)的意思.
然而,现在这个短语用的更多的意思是“to have learned or succeeded in something which might be an advantage in the future“,即【掌握或获得了某种有益或有利的东西 (如技能、知识】.
Now that you’ve got all of that under your belt：
【既然你已经都明白/掌握这些事情了】
Under your belt 例子:
You've got loads of experience under your belt.你拥有许多经验.