There are a few different ways you can move around 3D models in order to place them where you like. There is a comprehensive video for using 3D models, including moving them around, in the 'Using iSee' series you can see here.
Snap Mode:
The simplest way is to click and hold down the left mouse button anywhere on the object and just drag it around. This is called 'Snap Mode' as the object will automatically orient and snap itself to whatever surface the mouse is hovering over. This is simple and easy, but be careful not to accidently click on models you have placed using one of the other techniques or you may activate this mode and snap the model back to the nearest surface which can be irritating.
Snap Mode can save a lot of time and effort provided your 3D model is oriented properly when saved. When saved as a .glb file in Paint3D the model will snap in the same orientation as you see it. However, when saved as an .obj file in Tinkercad the model will save in an orientation where the bottom in iSee is in a plane perpendicular to the model base in Tinkercad. This may mean you will need to re-orient orient your model by 90 deg before saving to have it import to the most convenient snap view orientation. Alternatively you may want to export the model in more than one orientation deliberately so that you have separate versions that are optimized for snapping onto either the walls or the floor.
Free Move:
If you don't want the object to snap to a surface you can use 'Free Move'. To activate just left click and drag on the blue square in the centre of each face. This will let you reposition the object anywhere in a plane parallel with the face the square is on. In this mode you can lift the model off the ground or even move it into other models or terrian.
Resizing:
To resize, simply click and drag with the left mouse button on one of the blue cubes at the corner of the blue wireframe. Resizing only changes the size of the whole model, it's not possible to change the model's aspect ratio.
Rotating:
To rotate an object, click and drag with the left mouse button on the light blue spheres on each edge of the wire frame. This will rotate the model around the axis of the edge you have selected.