Present participle

To form the present participle, simply add -d to the infinitive.  It usually functions as an adjective and takes the nomal adjective endings.  Sometimes they are used like present participles in dependent clauses as in English, but this is rare and almost never used in spoken German.

kochendes Wasser  boiling water
die führenden Kritiker  the leading critics

Als ob/ Als wenn

The conjunctions als wenn and als ob are interchangeable; they both mean "as if" or "as though."  Both introduce a dependent clause, so the conjugated verb must go to the end.  In addition, both require the subjunctive II.

Als ob ich das nicht wüßte!  As if I didn't know that!
Er tut, als wenn er nichts Besseres zu tun hätte.  He acts as though he had nothing better to do.

Future Perfect

The future perfect tense is comparable to the other perfect tenses.  It is formed with the future of haben or sein, and the past participle.  The future perfect deals with the future as if it were already past time (he will have done it), or it is used to imply probability (that was probably him.)  The latter case commonly uses the past tense in English though.

Er wird gegangen sein.  He will have gone.
Ich werde es genommen haben.  I will have taken it.
Es wird dunkel geworden sein.  It will have become dark.
Das wird Rudi gewesen sein.  That will have been Rudi. / That was probably Rudi.

When using modals, the future perfect tense can create the double infinitive construction, so make sure to put the double infinitive at the very end.

Die Uhr wird sehr viel haben kosten müssen.