I have created models of a part that I created in Corel CAD. I have been trying to add texture to the parts but I can't get it to look the way I want it too. The parts are made of wood. Since the part is made of different pieces of wood. I am trying to get the wood grain pattern on the part to go in the right direction. when I unwrap the UVs only a couple of areas look the way I want them too. I have been trying to create faces on my models to separate the areas where the wood grain is going in a different direction but I haven't been successful. I am importing my models as STL files and trying to edit the mesh but nothing seems to work. Can anyone help me?
Your immediate concern
You want to unwrap the model but when you unwrap a model by default it is trying to give you what it thinks is the best two dimensional projection it can for the model you provided.
If you want to have the wood grain aim a certian way you will need to manually rotate the UV "Islands" in the uv editor to match the orientation you want. You may also need to scale or translate the islands so that the grain looks the same size etc.
Selection of Individual UV Islands
By default, the UV editor will only show the UV map for faces that you have selected in edit mode. This can be used to your advantage.
Select the faces that you want to have the wood grain oriented in a particular way in the 3d editor window.
Select the areas you want to modify in the uv editor. To have the effect you want, you will need to select whole faces.
In uv editor window and you can use R to rotate, S for scaling and G to translate the UV islands in the image editor.
You can choose from several "uv selection modes" in the uv editor, but the default is vertex so I will assume you are using that mode.
If you select only faces you want to rotate at once from the 3d view, you can use A in the UV window to select the UV islands for them.
You might also find CTRL + L useful. This shortcut selects every visible "linked" piece of geometry. It works in the 3d view or on the UV editor. So if you select one of the vertices in the uv editor and press that combination of keys, you will select all the linked UV islands.
Blender is very useful and fun software but it does have some learning curve to it. It sounds like you might be new to UV editing in blender as well.
In addition to this answer I'd recommend looking for some tutorials on the topic because they might help you in the long term.
Blender Guru (AKA Andrew Price) has a tutorial in some of his begginners series that is pretty useful for understanding some of how to unwrap particular kinds of geometry.
Here is a link: Begginer UV tutorial