1. Paper Collages
This is any collage that is made using paper as a medium, however various different types of paper can be used, either solely one type or a combination of different paper. Some popular paper types used are: photos, magazines, newspaper, envelops, design-printed paper, textured paper & coloured cardboard. Paper collages can be constructed in a variety of ways, the paper can be cut randomly or specific things can be cut out, or it can be ripped & glued to paper, canvas or an object, in layers, randomly or to create a specific design. There are endless possibilities with paper collages, anything goes.

2. Paint Collages
This type of collage generally involves painting a sheet of paper with the paint or dye colour of your choice, make it interesting by painting a gradient of that colour, or add spots or stripes, use can even you spray paint. Set it aside to dry, then cut or tear the paper & glue it to the surface of your choice, paper, cardboard, cards, canvas, even lampshades or jewellery. You can even paint multiple pages with various different colours & combine them together on your chosen surface.

3. Wood & Natural Collages
There is always twigs, branches & leaves available to why not make use of them? You can create wonderfully effective collages with driftwood, twigs, leaves, flowers, raw or polished wood or even shells. Additionally these collages are great for children as they involve a variety of different textures, but don’t be fooled, adults have have great fun with this too & create very refined pieces.

4. Fabric Collages
These collages are great for all those leftover scraps you may have lying around or even old clothes. Pieces can be cut or ripped into shapes or strips & arranged in a design you find appealing. Depending on the material it can either be glued down, ironed on, hand stitched or sewn (using a sewing machine) onto your chosen surface. Additionally embellishments like buttons or ribbons could be added as well. If you’re feeling adventurous you could even trying felting a collage, this is a technique where raw or coloured wool fibres are blended together, using soap & working or rubbing the wool until it is blended together. 

5. 3D Collages
The majority of collage types above have aspects about them that are 3D, however you could also make a whole collage 3D by using materials like buttons & layering them. These collages can be a bit fiddly but the result is well worth it. Another technique that could be used to create a 3D collage are to create a 2D collage first, it would probably be best to use paper only, then cut into the collage a triangle, BUT only cut TWO of the three side, then fold the triangle over on the uncut side. This may take a little trial & error to get just right. Finish by sticking another piece of paper underneath the collage so it shows through the holes you’ve made.

6. Mosaics
Now, I bet you didn’t realise that mosaics are a type of collage. The most common materials used are stone, glass, tiles, pebbles & marble & can be in the form of stain-glass windows, steeping stones, wall hangings or table tops. Mosaics are becoming increasingly popular in Primary Schools because they make fabulous collaborative art projects, where everyone can contribute, which are usually created in the form of totem poles, murals or steeping stones. To make one of these you first need to decide what you’ll be creating, one great idea is the border of a mirror, you’ll also need some tiles or similar materials & some pretty heavy-duty cement or grout to hold it together.

7. Découpage
This type of collage involves using flat materials, such as linoleum, plastic or decorative paper, like wrapping paper  & gluing it to an object of your choice, something like an old-school telephone, plate, bowl or clock. Then a lacquer or varnish which dries clear must be applied over the top, to stop any paper peeling off & to slightly preserve it against general wear & tear.

8. Digital Collages
This type of collage is a testament to how far technology has come, there are many programs & websites out there which will allow you to make a collage of digital images, either from a standard gallery or by uploading your favourite pictures or personal photographs. 
Majority of these programs allow you to crop, mirror, duplicate, move, colour, frame & edit your chosen images, as well as some allowing you to choose the order in which you layer your images. Some websites which aid in digital collages are: Shape Collage (www.shapecollage.com), Polyvore (www.polyvore.com) & SmileBox (www.smilebox.com). Then at the touch of a button you can print your creation, to mix it up a bit you can print onto coloured or decorative paper, so you have a funky background, instead of plain old white. 

 
Source: https://creatingartadventures.weebly.com/types-of-collage.html