How to interpret OSRM results

[Lambo2020]

Hi

Pls refer to website:
https://project-osrm.org/docs/v5.24.0/api/#trip-service

When I paste the below code:
"http://router.project-osrm.org/trip/v1/driving/13.388860,52.517037;13.397634,52.529407;13.428555,52.523219;13.418555,52.523215?source=first&destination=any"

Question 1:
What is the meaning of waypoint_index": 0"?
Does it mean that the point: "13.388798, 52.517033" is the first coordinate aka starting point?

Question 2:
Why is it ""distance": 4.231521214," in the result?
What does this distance represent?
Does it equate to the distance between the required first coordinate (13.388860,52.517037) and the actually mapped first coordinate (13.388798, 52.517033)?

Question 3:
So does that mean that the OSRM does not use the exact first coordiante that I asked it to use?
Whys is this so?

How do I interpret the bolded section of the results shown below by answering my questions above posted:

{
"code": "Ok",
"trips": [
{
"geometry": "mfp_I__vpAk~@xHgGgg@{DwWq@cf@lG{m@bDiQrCkGqImHs@cY~BcP@sDb@e@hD_LjKkRt@InHpCDFFpL[rD}BzK{GnUzOrQbCpBZu@}CkDPi@kCuCk@m@Of@{@w@iGyHgKn[dTnXnEIdOh_@pEbJvAtEvDzOtBl_A@b@VC",
"legs": [
{
"steps": [],
"summary": "",
"weight": 263.2,
"duration": 260.3,
"distance": 1886.8
},
{
"steps": [],
"summary": "",
"weight": 370.4,
"duration": 370.4,
"distance": 2845.4
},
{
"steps": [],
"summary": "",
"weight": 163.5,
"duration": 163.5,
"distance": 1344.3
},
{
"steps": [],
"summary": "",
"weight": 323.2,
"duration": 322,
"distance": 2921.4
}
],
"weight_name": "routability",
"weight": 1120.3,
"duration": 1116.2,
"distance": 8997.9
}
],
"waypoints": [
{
"waypoint_index": 0,
"trips_index": 0,
"hint": "PPwJgDHgm4UXAAAABQAAAAAAAAAgAAAAIXRPQYXNK0AAAAAAcPePQQsAAAADAAAAAAAAABAAAACdCAEA_kvMAKlYIQM8TMwArVghAwAA7wojejYY",
"distance": 4.231521214,
"name": "Friedrichstraße",
"location": [13.388798, 52.517033]
},
{
"waypoint_index": 1,
"trips_index": 0,
"hint": "eP7dgW2djIcGAAAACQAAAAAAAAB3AAAAppONQCyhu0AAAAAA1J-EQgYAAAAJAAAAAAAAAHcAAACdCAEAfm7MABiJIQOCbswA_4ghAwAAXwUjejYY",
"distance": 2.795148358,
"name": "Torstraße",
"location": [13.39763, 52.529432]
},
{
"waypoint_index": 2,
"trips_index": 0,
"hint": "QSUYgP___38fAAAAUQAAACYAAABSAAAAeosKQlNOX0Ki6yZCakq4Qh8AAABRAAAAJgAAAFIAAACdCAEASufMAOdwIQNL58wA03AhAwQAvxAjejYY",
"distance": 2.226580806,
"name": "Platz der Vereinten Nationen",
"location": [13.428554, 52.523239]
},
{
"waypoint_index": 3,
"trips_index": 0,
"hint": "j6Pkgf___3_XAAAAHAEAADEAAAAAAAAAe5ezQqdY40HN5KNBAAAAANcAAAAcAQAAMQAAAAAAAACdCAEAe7_MABxxIQM7wMwAz3AhAwIAHwIjejYY",
"distance": 15.595935657,
"name": "",
"location": [13.418363, 52.523292]
}
]
}