When you tween with the timeline, start by placing your object on the stage at the beginning point, then select the first frame on the objects layer of where you want the tween to begin, select add tween, the tween should appear in that layer as a solid blue line of several added frames, if you wish to place multiple "points" along the tween, then you select the frame down timline within that tween block where that event occurs, then drag the object to the next point (prior to the end of the tween), a diamond should appear in the tween at that frame, then select the next point/frame down the timeline, then drag object, another diamond will appear there, then choose last frame of tween timeline, and drag object to end point of tween.
It is very important to choose those points on the tween layer before moving the object, currently it appears what you are doing is ignoring the timeline and trying to drag an object around at the end point of the tween.
The above advice is good. It sounds like you have created some kind of motion path, and you are wanting to further edit it. There are many ways to edit, and some will work out better than others. Editing a motion path differs greatly depending on what kind of path you have.
1) If you started with a path where you have pasted, say, a stroke as your path (you drew something with the pencil or pen, and pasted it onto your tween), you will be dealing with a lot of auto-generated keyframes -- especially if you used a pencil line instead of a pen line. If you drag your object around, where those keyframes are will affect the resulting path. What to do: Try to modify the path using the Pen tools, or start with a pen drawn path. This way you have fewer keyframes to accomodate for. If you have a pencil-drawn path, try removing keyframes and then adjust the path using beziers. Alternatively, paste the motion path as a raw path on a new layer, adjust it by bending, and then repaste it onto the tween.
When you ask Flash to auto-keyframe a pasted path, there's really no way around this. Flash has to create keyframes for you, and isn't able to know how you may want to further edit it. So the above ways are necessary, and unfortunately it's a bit of work whatever way you go.
2) You may have a path that you have curved, but you want a linear path "down the road" (later on the tween). In this case, the motion tween is inserting curve property keyframes, because you have curved the path. To make the line straight, you need to convert the points to linear points. You can do this on the path or in the motion editor using the Convert Anchor point tool. Or, you can go in the motion editor, right-click the keyframes and choose "Corner point" or Linear Left/right as needed.
3) You applied an ease and you're dragging the instance on the Stage. This can be tricky. What you've asked Flash to do when applying an ease is for motion math to take over an animate the position of the instance in relation to values (the original path). The instance is controlled by the ease, and Flash accomodates each time you move it. Oftentimes you can't really tell what's going to happen, especially on the Stage (Flash is doing what's mathematically correct and necessary, but it might not be what you actually want!). In this case you probably want to turn off the ease, create your motion path, and then re-enable the ease and see how that affects the path. Adjusting your work in the motion editor might be easier, as you can see the dotted eased values in the graph, which tell you what's actually going to happen to the motion (the "real" value post-ease).
4) You used the transform panel or Free transform tool on the motion path, which gave wacky results and then you're moving the instance and things are getting worse. This is one area where motion paths can have less desirable results, as it's using a traditional tool not really designed for the new feature on a new feature. My recommendation is to avoid the transform panel, and use the Free Transform tool instead. In a nutshell, the Transform panel traditionally deals with shapes, and the motion path is not a traditional shape - so there are a lot of calculations swapping back and forth behind the scenes to try and give you what you want. Things can get wacky here, so if you already have something very complex (such as a pasted path with tons of keyframes), your transformations may not be what you actually wanted. Free Transform is better, or even better, manually adjust the beziers. Another alternative is to, again, copy the motion path as a static raw path, transform it and make your adjustments, and repaste it onto your tween.
Let me know if you need additional help, or are running into something else entirely.