How can we gain more attention from students inside the classroom especially for those who do not want to learn due to lack of motivations?

Respect your students and try to love them even they do somthing wrong, try not to threat them after asking for their attention and you did not get it,Your students, whether preschool, elementary, or high school, will rise to meet whatever expectation you set for them—as long as you clearly show them how.
The signal you use is up to you, but I recommend a simple verbal cue like, “Can I have your attention?” I like this because it communicates exactly what you want and can be used anywhere.
You can also use a manufactured sound like a squeak toy, a Snapple cap, a train whistle, or any sound you like.
Follow these steps to get your students’ attention quickly and without difficulty.
 

If the teacher is excited about teaching the students, then naturally the students will be excited about learning. If a class is unmotivated, moody and has constant bad attitudes, then perhaps the attitude of the teacher needs to be investigated.

 

Learning differentiation and the teacher’s attitude is the key to motivating students.  If Teachers make and effort in accommodating students with diverse teaching, learning differentiation, active  learning strategies, special needs, ESL and preferred learning styles, then the motivation of  students just happens naturally.   

<p>make the lesson funny</p>

Often, no way.
Just admonish them, since they are not and will not be motivated at all.
Maybe, best way is to ask thm why they are here and what they want.
If they show lack of interest and attention, the best way is to try and explain them that maybe they do not need to be here at all and will accomplish more in some other spheres