Learn Swedish: Hon ska hämta vännen ikväll. - She is going to pick up the friend tonight.

Because of the word ska, which indicates a future plan ("is going to" or "will"). After ska, you always use the dictionary form (the bare infinitive) of the following verb, which is hämta.

Can I use hämta if I want to pick up an object from the floor?

No. hämta specifically means "to fetch" or to collect someone or something from a location. If you are physically lifting an item off the ground, you would use a different phrase like plocka upp.

Why does the word vännen have a double "n"?

The base word for "friend" is vän. To say "the friend", we add the "the" ending for en-words, which is -en. When we add it, the "n" doubles to make vännen. This doubling is a common Swedish spelling rule to ensure the "ä" vowel stays short.

Does ikväll mean "this evening" or "tonight"?

It can mean both! Swedish doesn't have a separate everyday word specifically for "tonight". You use ikväll (which literally translates to "in evening") to talk about the upcoming evening or night of the current day.