alger
The Spanish word 'alfiler' does not translate to 'alger' in English. It directly translates to 'pin' in English. It's typically used to refer to a needle or short pointed piece of metal with a head, which is used in sewing to fasten pieces of fabric together. It can also refer to safety pins, which are made slightly differently but have a similar use.
I lost a pin on the floor of my room.
This sentence implies that the speaker lost a pin, likely a small pin used for fastening items such as clothes, somewhere on the floor in their room. The verb 'perdí' is the first person past tense of 'perder', meaning 'to lose'.
Hold the pattern to the fabric with a pin before cutting it.
This sentence is a command asking someone to use a pin to fasten a pattern to the fabric. It is advice directed at someone who is about to cut fabric, presumably for sewing or some other craft. The verb 'sujeta' is a command form of 'sujetar', which means 'to hold' or 'to attach'.
The pin that I used for the map fell off.
This sentence explains an event where a pin that was used for marking something on a map has fallen. 'Se cayó' is the reflexive form of 'caer', meaning to fall, usually used to signify that something fell down by itself or without being pushed.