You can make lines and curves. This takes just a little extra time but once you do it a few times it gets kind'a easy. And you do have the COPY and PASTE at your finger tips. I will try and step you through it.
Make sure you have a clean canvas to work on and turn on the grid and snap to grid. Also adjust your canvas to 400%. All this will make life easier, but not really necessary, till you understand what you are doing.
Pick custom shape and make a line about 16 cells long across the screen. It should snap to the grid nicely if you get close enough to them. Make sure you hit the ESC key when done.
Now you have two points marked on the screen. Ignore the anchor point in the middle. In the composition panel click on the Outline color box. Use the eye dropper to select the color in the Fill Solid color box. That makes the object and outline color exactly the same. Adjust the Thickness of the Outline color to ".1" To see the line you created turn off the canvas grid. Or you could adjust the Outline Thickness to ".2" or greater. I would stick to .1 for this exercise if I could.
The object you just created starts where you first clicked the canvas and to the point you clicked the second position. You think you just made a line correct? No... When you hit the ESC key the software completes the object by using the last selected point and drawing a line to the starting point. Adjust the length using the know options available. You can cut and paste, rotate, change positions of the line. But to adjust the thickness please use the Outline Thickness for it works better for this.. This is a straight line only.
If you want to make a curved line you must glue the two lines together. The one you made and the one the computer made. You will simulate this by making both sides of the object move at the same time. In this example you are going to make the front half bend up and the rear half bend down. This requires you to place 4 vertexes to the object. Two in the center of the front half and two in the center of the rear half. Click on the object till you see the objects vertexes. Now right click on the object between the first vertex and the center of the line. Add the vertex. Now add a vertex to the line between the middle of the line and the end. Remember that you can always slide any vertex along the line till you get it right where you need it.
Now select both of the two added vertexes by holding down the Shift key while selecting each vertex. You are now going to move the object apart by moving one side down using the down arrow key on the keyboard. Both vertexes should move down at the same time. Tap the down arrow key 4 times, that should be enough. The object should look like a flat ellipse. Now is the time to add the second set of vertexes. You need to add the new vertexes right above the ones you have already made. Right across from them on the other side, so when you close up the ellipse they will be over top of each other. Add the vertexes the same way as before. Now close up the ellipse by using the up arrow key tapping it the same number of times you used on the down arrow key.
You should now have the line you made all back together but with some added vertexes. Now the magic comes in to play. You are going to select the front pair of vertexes by using the mouse. Do this by holding down the left mouse button and dragging a box around the front pair of vertexes. You are using the box because the two vertexes are on top of each other. This box looks like a dashed line and will disappear after you let the mouse button go. Now you can use the up arrow key to adjust the front bend on the line. Using your mouse again, select the rear pair of vertexes the same way. Use the down arrow key to bend the back half of the line down.
The handles on the vertexes might need to be adjusted to close up the line evenly if for some reason they spread. Or you can remove the control points by right mouse click on the vertexes and selecting Remove Control Points. Using Control points can take a while to get use to them. You can always ad the vertex back in to create that gentle bend.
Now this line can be animated in any way you like using the tools in Express Animate. If you need more bends just add more pairs of vertexes, You can adjust the length easy enough, but keep using the Outline Thickness to make make changes to the width. I like doing it that way and I can animate the thickness easier.
Here is a link to a quick video showing how it's done. It very crude but all the steps are demonstrated. https://youtu.be/8VgsT1CddNc
I hope you find this easy to follow. If you don't get it the first time try starting over. It does work and works very well. Let me know if you got it worked out or If you need more help.