Your 3D print job will be supplied to you with raft and supports. Raft helps the job stick to the print bed while printing, and supports ensure that overhangs and fine details print properly.

Raft typically peels away but if it sticks to the bottom of your job use pliers to gently pry it away from each corner of the print and then use a palette knife or scraper to separate the raft from the job. Be careful while doing this as the scraper can slip.

Support also typically peels away but you may need pliers or strong tweezers to pull it away from the various nooks and crannies in your job. You can also use a metal file or sandpaper to smooth out your job.

Assembly:

PLA plastic glues together well with super-glue. Acetone also works well to join PLA pieces together though you should be careful when using it as acetone is highly flammable. Hot glue guns tend not to work well as they require too much glue to work and are prone to melting the PLA.

PLA will also take screws if you design screw holes into your pieces or if you use a high enough infill percentage. Attempting to screw or drill through low-infill PLA jobs usually leads to fractured PLA.