It is such a basic thing I don't think I have mentioned it in any YouTube video's I have done, though I am often doing it without comment.
There are 2 ways of turning a piece of wood commonly called Spindle orientation and Bowl orientation spindle is where the grain of the wood runs along parallel to the bed of the lathe and is typically used in candlesticks, rolling pins, pens etc. Bowl is where the grain direction is across the bed and is typically used in bowls and the like.
Different tools are used in each orientation, get it wrong and it could be dangerous. Can you get along to one of the many AWGB clubs? where more tailored advice maybe a bit of instruction can be given?
https://www.awgb.co.uk/clubs/ I asked what you were trying to make as the advice I could give is completely different depending on the orientation of the wood on your lathe, you answered with 2 projects that are completely different orientations which makes giving you any specific answer safely an impossible task.
Lets start from the beginning. Choose spindle or bowl project, tell me how you intend to put it on the lathe from a reciprocating saw (which cuts much flatter than many of the natural edge blanks I start with by the way) what tools you have to use and how you intend to use the tool...
Better still go get an intro lesson from one of the many teachers around the country and you may save yourself months of failure and potentially serious injury even a small piece of wood at 1000rpm is potentially very dangerous.
As I said trimming up the ends between centres is very easy to do but there is myriad ways of doing it which depend on many factors. So your opening question is impossible to answer.