There around 15 types of mission you do. Each mission serves its purpose. Like in capture mission you pretty much run to the end of the map and capture the target and extract. But if you want to grind for exp then we generally do defence missions where we have to protect a still objective. Hence all the enemies come to us and we kill them for exp. The devs have developed the movement of character like that to give us the fast paced action where you can combo your movement how ever you like with your attacks. It like freedom trust me. After playing warframe for a while now, If I play any other game it feels pretty slow.(my personal taste, I’m not saying any game is good or bad in comparison to warframe)
But one thing I do want to brag about is the community. Its probably the best one out there. Unlike vainglory people are not toxic and just enjoy the game. Everyone is ready to help each other out, even the noobs are treated really well(personal experience).
Edit: Sorry I can’t really explain the how exp works but I will tell you why defence is best for exp grind. In WF you get exp from all the your teammates’ kills, but for that to happen they need to be in your proximity. Hence everyone is in proximity of each other and we can do multiple waves and get all the exp from all kills by each team member.