What is the 行 in 行有餘力？
行 here means "to do" or "to perform".

行：實行；實踐 to do; to perform; to practice
有：還有 still have
餘：多餘的 superfluous; surplus; excess
力：能力 ability; capability

行有餘力，
After doing these and still having surplus capability,

行有餘力，則以學文。
After one can perform the above things, and has enough time and ability, one should study and learn some knowledge.

"The above things" mean 入則孝，出則弟，謹而信，汎愛眾，而親仁.

Examples:  

先思而後行
Think before you act.
Look before you leap.

行之不懈
Do it with no remission.

反其道而行
Do it in an opposite way.

行之有年
Has been performed for years.

知行合一
Unity of knowledge and practice.

知之者不如行之者。
To do is better than to say.

言出必行
Do it after saying it.
No sooner said than done.

勢在必行
Must do it under such a circumstance.



親仁
親近君子 Close to the gentleman
親近有仁德的人 Close to benevolent people
「仁」指「仁者」kind, merciful, benevolent, kindly, charitable people