This is the 676th most frequent Japanese word.
便利
Convenient.
'便利' refers to the usefulness and practicality of the app.
このアプリはとても便利です。
This app is very convenient.
'便利' describes the advantages and accessibility of the location.
便利な場所に住んでいます。
I live in a convenient location.
'便利' modifies '道具' to describe tools that are functional and useful.