l'll assume you're asking for each numbers place value. 12,354.897 (I'll go from left to right)
1 is in the ten thousands place.
2 is in the thousands place.
3 is in the hundreds place.
5 is in the tens place.
4 is in the ones place.
8 is in the tenths place. (Notice the "th" at the end of ten here. Numbers behind the decimal end in "th". Also, there's no ones place behind the decimal)